An image forming apparatus includes a storage unit, a connector including a power supply terminal, a power supply unit for generating an operating voltage, a switch for turning on and off application of the operating voltage to the power supply terminal, a capacitor connected between the power supply terminal and the switch, and a control circuit configured to start up when a reset signal is changed. When the main power supply is turned on, the switch is temporarily turned on, and the reset signal is changed after the switch is turned off. After a start-up process is started, the control circuit interrupts the start-up process when recognizing that there is a connected device based on a result of comparison between a capacitor voltage and a threshold voltage.