PURPOSE: To improve the safety of a worker and to prevent destruction and deterioration in a measuring circuit and a semiconductor device by providing a sensor to detect whether a protecting device is set or not, and making measurement impossible unless it is set.

CONSTITUTION: A prober is provided with a sealed box 9 seving as a protecting device which covers a measurement system to prevent electric shock, a contact switch 10 serving as a sensor which is attached to the box 9 to detect the opened state of the box 9, and an electromagnetic relay 11 to turn ON-OFF an action for applying the output of a power source device 5 to a probe 3. In the case of measurement, when the box 9 is in an opened state, the switch 10 turns OFF to make the relay 11 turn OFF for not applying voltage to a probe 3. When the box 9 is closed, the switch 10 and moreover the relay 11 turn ON for making the measurement possible. Thus the provision of the switch 10 makes the measurement impossible unless the box is closed.