An image forming apparatus has a network interface unit for communication with an electronic mail server via a communication network, a main control unit that entirely controls the image forming apparatus and does not operate in a power-saving mode, and a sub control unit that inquires of the electronic mail server in the power-saving mode about whether an electronic mail addressed to the image forming apparatus is stored in the electronic mail server. When such an electronic mail is stored in the electronic mail server, the sub control unit activates the main control unit. The main control unit shifts the image forming apparatus from the power-saving mode to a normal mode, and acquires the electronic mail from the electronic mail server. An image forming unit forms an image on a recording medium based on an attachment file attached to the electronic mail acquired by the main control unit.