An external signal detection circuit includes an input port, to which a first end of a circuit including a pull-up resistor connected in series with a first switch portion is connected, the input port receiving an input of an external signal; an input detection portion connected to the input port for receiving an input of the external signal and an input of an input detection signal that sets a timing for intermittently detecting the input of the external signal; and a connection control portion turning on the first switch portion in time with the timing at which the external signal is detected.