diff --git a/input_spliter.go b/input_spliter.go
index da1ff5c..11516bc 100644
--- a/input_spliter.go
+++ b/input_spliter.go
@@ -24,13 +24,16 @@ func split(ctx context.Context, r io.Reader) (<-chan string, <-chan error) {
 		for sc.Scan() {
 			select {
 			case <-ctx.Done():
-				errc <- ctx.Err()
 				return
 			default:
 				l := sc.Text()
 				if isRootBlockBeginning(l) {
 					if len(block) != 0 {
-						blockc <- block
+						select {
+						case <-ctx.Done():
+							return
+						case blockc <- block:
+						}
 					}
 					block = ""
 				}
@@ -41,8 +44,12 @@ func split(ctx context.Context, r io.Reader) (<-chan string, <-chan error) {
 			errc <- err
 			return
 		}
-		blockc <- block // 最後のRootブロック送出
-		return
+		select {
+		case <-ctx.Done():
+			return
+		case blockc <- block: // 最後のRootブロック送出
+			return
+		}
 	}()
 
 	return blockc, errc
diff --git a/pipeline_tree_grower.go b/pipeline_tree_grower.go
index 4c7808d..3e7c829 100644
--- a/pipeline_tree_grower.go
+++ b/pipeline_tree_grower.go
@@ -57,7 +57,11 @@ func (dg *defaultGrowerPipeline) worker(ctx context.Context, wg *sync.WaitGroup,
 				errc <- err
 				return
 			}
-			nodes <- root
+			select {
+			case <-ctx.Done():
+				return
+			case nodes <- root:
+			}
 		}
 	}
 }
diff --git a/root_generator.go b/root_generator.go
index 5ea2e25..e7ebfa5 100644
--- a/root_generator.go
+++ b/root_generator.go
@@ -134,8 +134,11 @@ func (rg *rootGeneratorPipeline) worker(ctx context.Context, wg *sync.WaitGroup,
 				errc <- err
 				return
 			}
-
-			rootc <- root
+			select {
+			case <-ctx.Done():
+				return
+			case rootc <- root:
+			}
 		}
 	}
 }
diff --git a/tree_handler_output_test.go b/tree_handler_output_test.go
index f9a2e69..dd1b733 100644
--- a/tree_handler_output_test.go
+++ b/tree_handler_output_test.go
@@ -10,6 +10,7 @@ import (
 	"os"
 	"strings"
 	"testing"
+	"time"
 
 	"github.com/ddddddO/gtree"
 	tu "github.com/ddddddO/gtree/testutil"
@@ -1192,3 +1193,15 @@ children:
 		})
 	}
 }
+
+func TestOutput_detecting_goroutinelerk(t *testing.T) {
+	ctx, cancel := context.WithTimeout(context.Background(), time.Duration(500*time.Millisecond))
+	defer cancel()
+	w := &strings.Builder{}
+	r := strings.NewReader(tu.TwentyThousandRoots)
+	if gotErr := gtree.Output(w, r, gtree.WithMassive(ctx)); gotErr != nil {
+		if gotErr != context.DeadlineExceeded {
+			t.Errorf("\ngotErr: \n%v\nwantErr: \n%v", gotErr, context.DeadlineExceeded)
+		}
+	}
+}