◯functions.php
function my_custom_post_type_archive_where( $where, $args ){
$post_type = isset( $args['post_type'] ) ? $args['post_type'] : 'post';
$where = "WHERE post_type = '$post_type' AND post_status = 'publish'";
return $where;
}
add_filter( 'getarchives_where', 'my_custom_post_type_archive_where', 10, 2 );
◯テンプレートファイル
$args = array(
'post_type' => 'POST_TYPE_NAME',
'type' => 'monthly',
'echo' => 0
);
$list = wp_get_archives($args);
echo '<ul>' . $list . '</ul>';