A comparator circuit compares a value of current detected by a current detector with a threshold. A first signal is output if the value is determined as to be equal to or more than the threshold. A second signal is output if the value is less than the threshold. Then, a logical operation is executed based on a signal output from the comparator circuit and the signal (oscillation signal, pause signal) output from a signal oscillator. When the power-shut off condition is met; i.e., the signal from the comparator circuit is the second signal and the signal from the signal oscillator is the pause signal, a turn-off control signal which turns off power supply to the power-supplying module is output to the oscillation output device, and a turn-on control signal which turns on the power supply to the power-supplying module is output to the oscillation output device otherwise.