diff --git a/sjplayer/src/sjplayer/CircleElement.d b/sjplayer/src/sjplayer/CircleElement.d
index f086ef6..dbaaf37 100644
--- a/sjplayer/src/sjplayer/CircleElement.d
+++ b/sjplayer/src/sjplayer/CircleElement.d
@@ -3,6 +3,7 @@ module sjplayer.CircleElement;
 
 import std.algorithm,
        std.conv,
+       std.math,
        std.exception;
 
 import gl4d;
@@ -34,7 +35,36 @@ class CircleElement : ElementInterface {
   }
 
   override DamageCalculationResult CalculateDamage(vec2 p1, vec2 p2) const {
-    // TODO:
+    if (!alive) return DamageCalculationResult(0, 0);
+
+    const m = matrix.transposed.inverse;
+
+    const a = (m * vec3(p1, 1)).xy;
+    const b = (m * vec3(p2, 1)).xy;
+    const s = b - a;
+
+    const s_length = s.length;
+    if (s_length == 0) {
+      // TODO: nearness calculation
+      return DamageCalculationResult(a.length < 1? damage: 0, 0);
+    }
+
+    const d = cross(vec3(s, 0), vec3(a, 0)).length / s_length;
+    if (d > 1) {
+      const nearness = (1 - (d-1).min(1f)).pow(2);
+      return DamageCalculationResult(0, nearness * nearness_coe);
+    }
+
+    const a_length = a.length;
+    const b_length = b.length;
+
+    const hit =
+      a.dot(s) * b.dot(s) <= 0 ||
+      a_length < 1 ||
+      b_length < 1;
+    if (hit) return DamageCalculationResult(damage, 0);
+
+    // TODO: nearness calculation
     return DamageCalculationResult(0, 0);
   }
 
diff --git a/sjplayer/src/sjplayer/Context.d b/sjplayer/src/sjplayer/Context.d
index 16578a6..3fd3724 100644
--- a/sjplayer/src/sjplayer/Context.d
+++ b/sjplayer/src/sjplayer/Context.d
@@ -81,7 +81,14 @@ class Context {
 
   ///
   ElementInterface.DamageCalculationResult CalculateDamage() const {
-    assert(false);  // TODO:
+    auto result = ElementInterface.DamageCalculationResult(0, 0);
+    elements_.
+      map!(x => x.CalculateDamage(actor_.pos, actor_.pos - actor_.speed)).
+      each!((x) {
+          result.damage   += x.damage;
+          result.nearness += x.nearness;
+        });
+    return result;
   }
 
   ///
diff --git a/sjplayer/standalone/main.d b/sjplayer/standalone/main.d
index c95ebea..f81259c 100644
--- a/sjplayer/standalone/main.d
+++ b/sjplayer/standalone/main.d
@@ -43,6 +43,14 @@ int main(string[] args) {
     context.actor.Update();
     context.posteffect.Update();
 
+    const dmg = context.CalculateDamage();
+    if (dmg.damage != 0) {
+      "damage: %f (%f)".writefln(dmg.damage, beat);
+    }
+    if (dmg.nearness != 0) {
+      "nearness: %f (%f)".writefln(dmg.nearness, beat);
+    }
+
     context.StartDrawing();
 
     context.DrawBackground();