A harness retaining device is disclosed for retaining a harness and causing the harness together with a connection element for an electric/electronic circuit to be supported with respect to a portion of a frame of a vehicle seat. The harness retaining device includes a support arm having first and second end portions, the first end portion of the support arm being engagingly connectable with the connection element, an anchor-like clip provided on the first end portion of the support arm, and a locking member provided on the second end portion of the support arm for fastening the harness. When the first end portion of the support arm is connected to the connection element and the anchor-like clip is fitted through the portion of the seat frame, the connection element and the harness are supported with respect to the portion of the frame of the vehicle seat through the support arm.