When a user presses down an extension directing button, a control unit of an image forming apparatus detects the press-down of the extension directing button and executes a setting process of new mode set time. In this case, the control unit calculates the new mode set time by adding extension time extracted from an extension time data storage unit to basic set time acquired from a basic set time data storage unit and records the new mode set time in a mode set time data storage unit. Then, when start of a sleep mode is detected, the control unit of the image forming apparatus records the basic set time, which is extracted from the basic set time data storage unit, in the mode set time data storage unit as new mode set time when the mode set time is extended.