PURPOSE: To detect a step-out without any loss of power at the time of detection by measuring abnormal sound generated at the time of step-out.

CONSTITUTION: This equipment is constituted of a driving-side magnet 15 and a driven-side magnet 16. The mechanism is that when the driving-side magnet 15 rotates, torque is transmitted to the driven-side magnet 16. A motor controller 11 rotates a motor 14 forwardly, reversely or stops the operation of the motor 14 and controls the number of rotations. A CPU 12 manages the operation of the motor controller 11 based on the data input from a microphone 19 and manages the operation of the microphone 19. The microphone 19 detects the sound pressure generated by a power transmitting mechanism and outputs it to the CPU 12. By this method, a step-out can be detected without any loss of the output of the stepping motor. Furthermore, voltage to be applied to the motor 14 can be set at such a level that the step-out may hardly occur and the motor 14 can be driven at that level. And, the reduction of the transmitted torque due to demagnetization or the appearance of abnormal sound can be avoided.