To solve the following problem: to measure insulation resistance of a motor or the like installed in a factory, a person in charge goes to a control center in the vicinity of the place where the motor is installed, and the person needs to reliably measure it at a non-covered spot of a cable, and the non-covered spot exists in a motor connecting terminal in a motor control box at the spot, so that it requires a great deal of labor to measure the insulation resistance of a number of motors.

A contactor has an insulation resistance measuring contact and a terminal, in which there are a new contact connected to a motor side cable and an external extraction terminal. Thereby, insulation resistance of the motor can be remotely and automatically measured.