An image forming apparatus operates in a power saving mode or in the normal printing mode. An image forming section forms an image in accordance with print data received from an external apparatus. A state detecting section detects a state of the image forming apparatus. A controller causes the image forming apparatus to enter into a power saving mode where the controller terminates supply of electric power to a section of the image forming apparatus that consumes a large electric power. A data detecting section detects whether the print data exists in the image forming apparatus. When the state detecting section detects a change in the state of the image forming apparatus and the data detecting section fails to detect print data in the image forming section, the controller causes the image forming apparatus to enter the power saving mode.