There is provided a technique of appropriately shifting an image forming apparatus to a power saving state in consideration of the use status of an external device such as a connected USB device. When a condition for shifting to a sleep state is satisfied, the CPU of the image forming apparatus determines whether or not a setting of a sleep shift at the time of use of the USB device is “permit”. If it is determined that the setting of the sleep shift at the time of use of the USB device is “do not permit”, the CPU determines whether or not the connected USB device is in use. If it is determined that the USB device is not in use, the CPU shifts the image forming apparatus to the sleep state.