A controller of an injection molding machine stores used/unused information in relation to each of the maximum number of controllable servo amplifiers, outputs an interruption request signal requesting power interruption in a lump to apart of or all of these plurality of servo amplifiers, and receives a power interruption confirmation signal confirming that the motor power of the servo amplifiers is interrupted. Further, the controller determines, on the basis of the interruption request signal, the power interruption confirmation signal and the used/unused information, whether or not interruption driving the servo motor is normally operated.