According to one embodiment, the power supply management portion includes a timer configured to output an ON signal every time set by the control circuit, an OR circuit configured to receive supply of an output signal from the timer, an external signal supplied from outside, and a switch control signal output from the control circuit, and a switch circuit configured to switch output of the power source voltage from an external power source according to an output signal from the OR circuit, and the control circuit turns on a switch control signal after confirming which of the output signal from the timer or the external signal has turned on the switch circuit and turns off the switch control signal when both of the output signal from the timer and the signal supplied from outside are turned off.