PURPOSE: To safely measure the insulation resistance of a resistance body in a motor by providing switching command means cutting off an insulation resistance measuring instrument from the motor before the operation of current supplying means for the motor according to a stop confirming signal for an elevator, and opening/closing means operating in accordance with the switching command.

CONSTITUTION: When the elevator is in the stopping state without any call at the time arriving at the measurement, the output signal of a detector 8 for stopping state without call and the output signal of a detector 9 for start are monitored by a control storage circuit 7 and a relay driving circuit 10 is exerted by the output signal of and AND circuit 16, then a stop synchronizing relay 15 is energized to make a contact 15a to be ON, a start synchronizing relay 18 is dienergized and a connected relay 20 is energized. A timer relay 21 is thereby energized and the insulation resistance measuring instrument 4 is connected to the motor 1. When the measurement is finished, the relay driving circuit 10 is made to stop the operation and the connected relay 20 is dienergized. The insulation resistance measuring instrument 4 is thereby cut off from the motor 1 to recover the timer relay 21. With such anarrangement, the insulation resistance of resistance body in the motor can be safely measured.