To permit highly efficient underwater propelling by utilizing a propelling system using vibrations of fin of aquatic mammals, where the lift acts on the fin, and making the cross section containing the body and the tail manubrium to be the wing shape so that a suppressing angle that may be created through vertical movement of the tail manubrium against the relative water flow.

The exterior shape consists of a body portion 1, a tail manubrium portion 2 and a tail fin portion 3. The body portion 1 is structured in a streamline form enclosing the body of a diver, with the body portion 1 disposed of a motor 4 for vertical movement of the tail manubrium 2. Moreover, when the equipment is moved forward, the drive switch is turned on and via a motor drive unit 5 a tail manubrium portion 2 is moved vertically by phase-controlled rotation of the motor 4 for the body portion 1 and a motor for the tail fin. Accordingly, the tail fin portion 3 thrusts the water, and the equipment moves forward by reaction thereof. Following the vertical movement of the tail fin 3, a suppressing angle against the relative water flow is created. The equipment is propelled effectively with the traveling direction component of the lift as the propelling force.