An image forming apparatus which is connected to a host apparatus, the image forming apparatus including a first memory, a second memory, a universal serial bus (USB) interface to receive a USB control signal or a USB data signal from the host apparatus, and a central processing unit (CPU) operating in a normal mode using the first memory or a power saving mode using the second memory. If the USB data signal is input in the power saving mode, the CPU activates the first memory and converts the power saving mode into the normal mode, and, if the USB control signal is input in the power saving mode, the CPU retains the power saving mode and performs an operation corresponding to the USB control signal using the second memory. Accordingly, the power saving mode is realized effectively.