This invention relates to a "swimming exercise device", which includes a device body, a pendulous device, two arm stroke gears and two elastic devices. The body includes a front portion and a rear portion; one end of the front portion is coupled to one end of the rear portion; a space is formed between the front portion and the rear portion. The pendulous device is disposed in the space, one end thereof is pivoted on the front portion and the other end thereof is pivoted on the rear portion. The arm stroke gears are respectively on the top of both sides of the front portion of the body and the elastic devices are respectively pivoted on the upper edge of the rear portion of the body.