diff --git a/.bin/music/test-60bpm.sj b/.bin/music/test-60bpm.sj
index d076722..ed55e79 100644
--- a/.bin/music/test-60bpm.sj
+++ b/.bin/music/test-60bpm.sj
@@ -18,14 +18,17 @@ posteffect [0..1] {
   clip_left  := 0.1;
   clip_right := 0.1;
 }
+variable [0..3.5] {
+  hoge = 1-time;
+}
 
-$repeat i 1 {
+$repeat i 2 {
   $repeat j 20 {
-    circle [$i..$i+2] {
+    circle [$i+1..$i+3] {
       color_r := 0.8;
       color_g := 0.1;
       color_b := 0.1;
-      color_a := 1;
+      color_a  = hoge;
 
       damage       := 0.1;
       nearness_coe := 0.01;
diff --git a/sjplayer/src/sjplayer/AbstractScheduledController.d b/sjplayer/src/sjplayer/AbstractScheduledController.d
index 369beb5..d3f4f66 100644
--- a/sjplayer/src/sjplayer/AbstractScheduledController.d
+++ b/sjplayer/src/sjplayer/AbstractScheduledController.d
@@ -74,8 +74,7 @@ abstract class AbstractScheduledController : ScheduledControllerInterface {
     }
     auto temp = varstore_[name];
     if (!temp.isNull) return temp;
-    // TODO: std constants
-    return Nullable!float.init;
+    return StandardVarStore.GetByName(name);
   }
   void SetParameter(ref in Parameter param, ref in VarStore vars) {
     if (param.name.length < 2 || param.name[0..2] != "__") {
diff --git a/sjplayer/src/sjplayer/Context.d b/sjplayer/src/sjplayer/Context.d
index 28387f0..3a39a92 100644
--- a/sjplayer/src/sjplayer/Context.d
+++ b/sjplayer/src/sjplayer/Context.d
@@ -21,7 +21,8 @@ import sjplayer.Actor,
        sjplayer.PostEffectControllerInterface,
        sjplayer.ProgramSet,
        sjplayer.ScheduledControllerInterface,
-       sjplayer.VarStore;
+       sjplayer.VarStore,
+       sjplayer.VarStoreScheduledController;
 
 ///
 class Context {
@@ -55,6 +56,10 @@ class Context {
           "circle",
           CircleElementScheduledControllerFactory(programs, varstore),
         ),
+        tuple(
+          "variable",
+          VarStoreScheduledControllerFactory(varstore),
+        ),
       );
     foreach (ref factory; factories) {
       factory[1].
diff --git a/sjplayer/src/sjplayer/VarStore.d b/sjplayer/src/sjplayer/VarStore.d
index 24d69b6..2408681 100644
--- a/sjplayer/src/sjplayer/VarStore.d
+++ b/sjplayer/src/sjplayer/VarStore.d
@@ -21,10 +21,19 @@ class VarStore : VarStoreInterface {
       case "actor_x": return Nullable!float(actor_.pos.x);
       case "actor_y": return Nullable!float(actor_.pos.y);
 
-      default: return Nullable!float.init;
+      default:
     }
+    return name in user_vars_?
+      Nullable!float(user_vars_[name]): Nullable!float.init;
+  }
+
+  ///
+  void opIndexAssign(float value, string name) {
+    user_vars_[name] = value;
   }
 
  private:
   const Actor actor_;
+
+  float[string] user_vars_;
 }
diff --git a/sjplayer/src/sjplayer/VarStoreScheduledController.d b/sjplayer/src/sjplayer/VarStoreScheduledController.d
new file mode 100644
index 0000000..fe0dcc5
--- /dev/null
+++ b/sjplayer/src/sjplayer/VarStoreScheduledController.d
@@ -0,0 +1,56 @@
+/// License: MIT
+module sjplayer.VarStoreScheduledController;
+
+import std.range.primitives;
+
+import sjscript;
+
+import sjplayer.AbstractScheduledController,
+       sjplayer.ContextBuilderInterface,
+       sjplayer.VarStore,
+       sjplayer.util.Parameter;
+
+///
+class VarStoreScheduledController : AbstractScheduledController {
+ public:
+  ///
+  alias VarStore = sjplayer.VarStore.VarStore;
+
+  ///
+  this(VarStore varstore, in ParametersBlock[] operations) {
+    super(varstore, operations);
+    varstore_ = varstore;
+  }
+
+  override void SetParameter(
+      ref in Parameter param,
+      ref in AbstractScheduledController.VarStore vars) {
+    const x_nullable = varstore_[param.name];
+    auto  x          = x_nullable.isNull? 0f: x_nullable.get;
+    param.CalculateParameter(x, vars);
+    varstore_[param.name] = x;
+  }
+
+ private:
+  VarStore varstore_;
+}
+
+///
+struct VarStoreScheduledControllerFactory {
+ public:
+  ///
+  this(VarStore varstore) {
+    varstore_ = varstore;
+  }
+
+  ///
+  void Create(R)(R params, ContextBuilderInterface builder)
+      if (isInputRange!R && is(ElementType!R == ParametersBlock)) {
+    auto product = new VarStoreScheduledController(
+        varstore_, SortParametersBlock(params));
+    builder.AddScheduledController(product);
+  }
+
+ private:
+  VarStore varstore_;
+}
diff --git a/sjscript/src/sjscript/calculate.d b/sjscript/src/sjscript/calculate.d
index 327187c..04b3693 100644
--- a/sjscript/src/sjscript/calculate.d
+++ b/sjscript/src/sjscript/calculate.d
@@ -7,6 +7,7 @@ import std.algorithm,
        std.format,
        std.math,
        std.traits,
+       std.typecons,
        std.variant;
 
 import sjscript.Expression,
@@ -22,12 +23,17 @@ static assert(IsVarStore!(float[string]));
 struct StandardVarStore {
  public:
   static float opIndex(string name) {
+    const v = GetByName(name);
+    enforce(!v.isNull);
+    return v.get;
+  }
+  static Nullable!float GetByName(string name) {
     switch (name) {
-      case "PI":   return PI;
-      case "PI_2": return PI_2;
-      case "PI_4": return PI_4;
-      case "E":    return E;
-      default: throw new Exception("undefined variable %s".format(name));
+      case "PI":   return Nullable!float(PI);
+      case "PI_2": return Nullable!float(PI_2);
+      case "PI_4": return Nullable!float(PI_4);
+      case "E":    return Nullable!float(E);
+      default: return Nullable!float.init;
     }
   }
   static assert(IsVarStore!StandardVarStore);