A swimming auxiliary device includes an attaching member an attaching member mounted to the swimmer's calf or forearm, and a connecting device connected to the attaching member so as to pivotally connect a web member to the attaching member. A pulling device is connected between the web member and the attaching member to pull the web member toward the attaching member. When the swimmer pushes the water, the water flows between the web and the attaching member so that the web member is pivoted away from the by the water. The web member is then pulled by the pulling device to return its original position again when the water flows away from the web member.