diff --git a/lib/typeprof/core/ast/control.rb b/lib/typeprof/core/ast/control.rb
index 82e1880d..2e64bdec 100644
--- a/lib/typeprof/core/ast/control.rb
+++ b/lib/typeprof/core/ast/control.rb
@@ -322,44 +322,74 @@ def install0(genv)
         ret = Vertex.new(self)
         @pivot&.install(genv)
 
-        # case文での型絞り込みを実装
-        if @pivot && @pivot.is_a?(LocalVariableReadNode)
-          var = @pivot.var
-          original_vtx = @lenv.get_var(var)
+        # Collect modified variables across all branches
+        vars = []
+        @when_nodes.each {|wn| wn.body.modified_vars(@lenv.locals.keys, vars) }
+        @else_clause.modified_vars(@lenv.locals.keys, vars) if @else_clause
+        vars.uniq!
 
-          # ダミー変数に元の型情報を設定
-          @lenv.set_var(:"*pivot", original_vtx)
+        # Save original variable vertices
+        saved_vtxs = {}
+        vars.each do |var|
+          saved_vtxs[var] = @lenv.get_var(var)
+        end
 
-          # 各when節を実行
-          @when_nodes.each do |when_node|
-            clause_result = when_node.install(genv)
-            @changes.add_edge(genv, clause_result, ret)
-            # 元の型に戻す
-            @lenv.set_var(var, original_vtx)
-          end
+        # Prepare per-branch result vertices
+        branch_vtxs = []
+
+        # Setup pivot narrowing if applicable
+        pivot_var = @pivot.is_a?(LocalVariableReadNode) ? @pivot.var : nil
+        if pivot_var
+          original_pivot = @lenv.get_var(pivot_var)
+          @lenv.set_var(:"*pivot", original_pivot)
+        end
+
+        # Install each when branch
+        @when_nodes.each do |when_node|
+          # Reset variables to original for each branch
+          saved_vtxs.each {|var, vtx| @lenv.set_var(var, vtx.new_vertex(genv, self)) }
+          @lenv.set_var(pivot_var, original_pivot) if pivot_var
+
+          clause_val = when_node.install(genv)
+          @changes.add_edge(genv, clause_val, ret)
 
-          # else節（他のwhen節で除外された後の型）
-          filtered_else_vtx = original_vtx.new_vertex(genv, self)
+          modified = {}
+          vars.each {|var| modified[var] = @lenv.get_var(var) }
+          branch_vtxs << [clause_val, modified]
+        end
+
+        # Install else branch
+        saved_vtxs.each {|var, vtx| @lenv.set_var(var, vtx.new_vertex(genv, self)) }
+        if pivot_var
+          # Apply exclusion filters for else
+          filtered_else_vtx = original_pivot.new_vertex(genv, self)
           @when_nodes.each do |when_node|
             when_node.get_exclusion_conditions.each do |static_ret|
-              # 各when節の型を除外（negation）
               filtered_else_vtx = IsAFilter.new(genv, self, filtered_else_vtx, true, static_ret).next_vtx
             end
           end
-          @lenv.set_var(var, filtered_else_vtx)
-          @changes.add_edge(genv, @else_clause.install(genv), ret)
-          @lenv.set_var(var, original_vtx)
+          @lenv.set_var(pivot_var, filtered_else_vtx)
+        end
+        else_val = @else_clause.install(genv)
+        @changes.add_edge(genv, else_val, ret)
 
-          # ダミー変数をクリア
-          @lenv.locals.delete(:"*pivot")
-        else
-          # pivotが変数でない場合は従来通り
-          @when_nodes.each do |when_node|
-            @changes.add_edge(genv, when_node.install(genv), ret)
+        else_modified = {}
+        vars.each {|var| else_modified[var] = @lenv.get_var(var) }
+        branch_vtxs << [else_val, else_modified]
+
+        # Join all branches
+        vars.each do |var|
+          joined = Vertex.new(self)
+          branch_vtxs.each do |branch_val, modified|
+            vtx = BotFilter.new(genv, self, modified[var], branch_val).next_vtx
+            @changes.add_edge(genv, vtx, joined)
           end
-          @changes.add_edge(genv, @else_clause.install(genv), ret)
+          @lenv.set_var(var, joined)
         end
 
+        # Cleanup
+        @lenv.locals.delete(:"*pivot") if pivot_var
+
         ret
       end
     end
diff --git a/scenario/flow/case_variable.rb b/scenario/flow/case_variable.rb
new file mode 100644
index 00000000..e74f0d6e
--- /dev/null
+++ b/scenario/flow/case_variable.rb
@@ -0,0 +1,20 @@
+## update
+def test(type, val)
+  case type
+  when :int
+    val = val.to_i
+  when :sym
+    val = val.to_sym
+  else
+    val = val
+  end
+  val
+end
+
+test(:int, "42")
+test(:sym, "hello")
+
+## assert
+class Object
+  def test: (:int | :sym, String) -> (Integer | String | Symbol)
+end