An image forming apparatus comprises a first circuit unit including a control unit and a second circuit unit having a driving unit. The apparatus generates, by a power-supply unit, a power-supply voltage necessary for driving the driving unit to supply the power-supply voltage to the driving unit. The apparatus detects a voltage reduction of the power-supply voltage and performs access stopping processing for stopping access of the second circuit unit, based on the detecting of the voltage reduction of the power-supply voltage.