a power supply apparatus controls the gate and drain power supplies at the rise time so that an output voltage of the gate power rises earlier than that of the drain power supply . another power supply control apparatus controls the gate and drain power supplies at the fall time so that an output voltage of the gate power supply fails later than that of the drain power supply . another power supply control apparatus turns off the drain supply of the fet among power supplies when it is detected by a voltage monitor whenever either of output voltages or the power supplies are not within said specified range .