The invention relates to an image forming apparatus that is capable of decreasing user wait time before it becomes ready for operation, by judging in an early stage if a person moves toward the image forming apparatus itself, and a power control method. A detecting area (205a) is formed for detecting if the person enters, the detecting area extending in front of the image forming apparatus body (10). According to the detectin result of the peak value of the signals output from a human body detecting sensor (202) when a person enters the detecting area and the judgement result of the judgement that whether the output signals, after the detected peak value, is reduced to an offset voltage, whether a person in the detecting area (205a) moves toward the direction approaching the image forming apparatus can be determined. The power supply mode is switched to the first operation mode if the power supply mode is found to be the second operation mode while it is judged that the person moves toward the image forming apparatus.