A comparator receives, on its second input terminal, a third anomaly threshold voltage from a threshold voltage generator, and outputs a low-level breaking indication signal to a control logic portion when a terminal voltage falls below the third anomaly threshold voltage. Three threshold setting resistors are serially connected between the source of a power MOSFET and a ground terminal. A divided voltage at the connecting point between the threshold setting resistors and is outputted as the third anomaly threshold voltage.