PURPOSE: To specify a leak point in a short time by providing an evacuation tube connecting an abutting unit and a vacuum generator, and a pressure sensor inserted in the way of evacuation tube.

CONSTITUTION: When the switch of a vacuum generator 5 is turned on to press the abutting face of a vacuum pad against an object 1, an abutting unit 2 and an evacuation tube 4 are evacuated. When the vacuum has reached a preset measurement starting vacuum, a solenoid valve 19 is closed to sustain vacuum state in the unit 2 and tube 4. When a pressure sensor 6 senses a measurement starting vacuum of -760mmHg, for example, a signal for closing the valve 19 is delivered immediately through a control circuit 23 and the measurement is started. A judging circuit 20 compares an electric signal (produced by converting the vacuum in the tube 4) from the sensor 6 with a signal received previously from an input means 21 and when it is judged that the electric signal is out of a set level, delivers a failure detection signal to an alarm 22.