PURPOSE: To improve positioning accuracy so that very correct hand operation can be conducted by making feedback of position detection signals of a forward end hand through an ultrasonic transmitter and a receiver to the control circuit of a hand driving part and controlling the position of a hand according to the signals.

CONSTITUTION: Detection signals of position detectors 51, 52, 53 installed on α, β, γ axes of a hand 5 are converted to ultrasonic signals to be transmitted by an ultrasonic transmitter 11, received by an ultrasonic receiver 12, and then converted to electric signals to be feedback to a control circuit 13 inside a control board. The control circuit 13 is so constituted as being capable of moving a hand 5 to a designated position and opening and closing the same to its control on the basis of three position signals in response to signals input from a control part, and the control signals of the control circuit 13 are sent to solenoid valves 14, 15, 16 respectively to open and close the solenoid valves 14, 15, 16, thereby driving α, β, γ axes driving motors is in rotation.