To improve manual operability by staying in standby in a closed loop circuit for short-circuiting mutual coils of a driving motor when a stool seat and a stool cover are put in an opening state and in an opening loop circuit when the stool seat and the stool cover are put in a closed state.

When driving force of a motor 11 is transmitted to a stool seat (a stool cover) 14 through a transmitting means 12 by a signal from the control part 10, the stool seat 14 rotates in the opening direction of the closing direction. A detecting means 15 for detecting an opening angle of the stool seat 14 is arranged on an output shaft 20 of the stool seat 14, and this detecting means 15 is composed of a magnet 22 and a Hall IC 23 arranged on an output shaft gear 21. A circuit is switched to Low from High by a signal from the Hall IC 23. Thus, in a standby state, the control part 10 switches a motor 11 to an open circuit after constant time when a signal from the Hall IC 23 is switched to High from Low, and switches the motor so as to becomes a short circuit after constant time when the signal is switched to Low from High.