diff --git a/Dockerfile b/Dockerfile
index 42181a1..cd2da33 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,7 +1,7 @@
 # Golang version defined in https://github.com/kaishuu0123/erd-go/blob/${ERD_VERSION}/go.mod#L3
 ARG ERD_GOLANG_BUILDER_TAG=1.15-alpine
 ARG A2S_GOLANG_BUILDER_TAG=1.20-alpine3.18
-ARG alpine_version=3.20.3
+ARG alpine_version=3.21.0
 FROM alpine:${alpine_version} AS base
 
 # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #
diff --git a/README.adoc b/README.adoc
index 781333e..12c3dd6 100644
--- a/README.adoc
+++ b/README.adoc
@@ -1,4 +1,4 @@
-:ALPINE_VERSION: 3.20.3
+:ALPINE_VERSION: 3.21.0
 :ASCIIDOCTOR_VERSION: 2.0.23
 :ASCIIDOCTOR_CONFLUENCE_VERSION: 0.0.2
 :ASCIIDOCTOR_PDF_VERSION: 2.3.19
diff --git a/tests/asciidoctor.bats b/tests/asciidoctor.bats
index 089e085..5687bba 100644
--- a/tests/asciidoctor.bats
+++ b/tests/asciidoctor.bats
@@ -1,7 +1,7 @@
 #!/usr/bin/env bats
 
 TMP_GENERATION_DIR="${BATS_TEST_DIRNAME}/tmp"
-ALPINE_VERSION=3.20.3
+ALPINE_VERSION=3.21.0
 ASCIIDOCTOR_VERSION=2.0.23
 ASCIIDOCTOR_CONFLUENCE_VERSION=0.0.2
 ASCIIDOCTOR_PDF_VERSION=2.3.19