When a fluid flow channel is interrupted while an electronic circuit unit 50 including a microcomputer 51 and the like receives electric source power, a flow control valve is displaced to a predetermined position closer to a first end of both ends of a motion range of the flow control valve in the fluid flow channel by a stepping motor 29. When the supply of electric source power is restarted after the supply of electric source power to the electronic circuit unit 50 is stopped, a predetermined number of pulses capable of displacing the flow control valve from the first end to a home position are supplied to the stepping motor 29 to displace the flow control valve to the home position with a second end of both ends of the motion range of the flow control valve being the home position of the flow control valve. Thus, the flow control valve is shifted to the home position while preventing occurrence of a disorder of the stepping motor, abnormal sounds and vibrations, in a simple configuration, without requiring means for detecting arrival of the flow control valve at the home position.