PURPOSE: To enable swimming and treading water to be freely performed on and under water even if legs are not sufficiently used, by providing the central section of a pair of left and right wing-shaped fins with a grip, and by providing root sections with holder sections for retaining arms.

CONSTITUTION: When arms 1 in front of elbows are retained by holder sections 3 and grips 2 are gripped, the arms in front of the elbows look like the fins of a humpback whale. When the elbows are attached to one's side under water in this state and the arms are oscillated symmetrically to the left and right within a surface orthogonal to the axial line of a human body, the fins 1 are moved like fans, and water is pushed toward legs, and by its reaction, the human body can advance in the head direction. The propelling force is different from normal paddling with palms in the state of crawl or breaststroke and is to be worked like a propeller within a surface orthogonal to the propelling direction, and reciprocating motion can be always used as the propelling force and the shapes of the fins 1 are formed to obtain a lift without disordering water flow, and so the human body can advance extremely easily at a high speed.