To obtain propulsion by vertically moving a tail fin by connecting a head part and a tail part of a plastic material to a body part by an elastic body skeleton, and extending-contracting a rubber tube.

A tail part 5 where a tail fin 6 and a foot stepping bar 7 are arranged is connected to a body part 3 by a rubber tube 9 and an elastic body skeleton 4, and a head part 1 where a handle 10, a pectoral fin type cover 11 to cover the handle and a pulley 12 are arranged is connected to the body part 3 by an elastic body skeleton 2. The handle 10 is gripped, and feet are placed on the foot stepping bar 7, and when kees are bent and stretched while keeping a longitudinal balance by a movement of one's body weight, the tail part 5 is vertically moved. Feet are placed on the handle 10, and a swimmer sits down on the body part 3, and when the handle 10 is gripped, pulled or returned, force is transmitted to the tail part 5, and the tail part 5 is vertically moved.