PURPOSE: To establish a complete fail-safe function and to warrant high speed and safety for a job by providing a zero cross synchronizing pulse signal generating means, a discrimination data storage means and a fault detection means to the controller so as to detect a fault of a semiconductor element automatically in the ON/OFF state of a load.

CONSTITUTION: When loads 15A, 15B are not driven in the clutch brake OFF state, input latch circuits 33A, 33B latch an OFF command signal from a drive operation panel 1 to turn off triacs 11A, 11B thereby allowing pulse signal generators 51A, 51B, 52A, 52B to output a zero cross synchronizing pulse signal. Thus, CPU 31A, 31B being a fault detection means compare a signal read by a control panel 30 with a discrimination data stored in memories 32A, 32B being discrimination data storage means so as to discriminate whether or not a fault takes place in the triacs 11A, 11B. In the case of brake ON state, an ON command given to the loads 15A, 15B is latched to the circuits 33A, 33B and an interrupt input from a power supply zero cross synchronizing circuit 20 is awaited.