To improve durability and to correctly learn by housing a motor and a crank arm for which a s tiding arm connected by a crank pin is attached to a crank shaft connected through a reducer inside a housing, fixing one end of a belt to the sliding arm and fixing the other end to the appropriate part of the housing.

The crank shaft 6 is connected through the reducer 5 to the motor 4 connected to a power source 2 housed in a battery case 3. The crank arm 7 attached to the crank shaft 6 is connected to the sliding arm 10 through the crank pin 8 and a connection arm 9. The attachment metal fitting 15 of the belt 14 is provided on the tip of the sliding arm 10 and the other end of the belt 14 is fixed to the side face on the opposite side of the sliding arm 10 of the housing 1. When the motor 4 is driven in a deceleration state and the crank arm 7 is rotated, the sliding arm 10 is moved back and forth inside the housing 1. Since the peripheral length of the belt 14 is changed accompanying it as well, the abdominal part of a body is tightened and loosened by prescribed rhythm.