An image forming apparatus including a photosensitive drum for forming a toner image, the apparatus comprising: a heating rotating body for heating a paper sheet with the toner image transferred; a heater for heating the heating rotating body; a controller (1, 5) including a control circuit (11, 51); and a power supply circuit for turning on and off power supply to the heater and the controller (1, 5), configured to supply power in one of a first supply mode, a second supply mode, and a third supply mode, the first supply mode being a mode for supplying power so that printing can be performed, and more power being supplied in the first supply mode than in the second supply mode or the third supply mode, more power being supplied in the second supply mode than in the third supply mode, the power supply circuit being configured to switch, in a period other than a predetermined specified period, from the power supply in the first supply mode to the power supply in the second supply mode when a predetermined first transition condition is satisfied, and to switch from the power supply in the second supply mode to the power supply in the third supply mode when a predetermined second transition condition is satisfied, and the power supply circuit being configured to switch, in the specified period, from the power supply in the first supply mode to the power supply in the second supply mode when the first transition condition is satisfied, and to maintain the second supply mode without performing the switching from the power supply in the second supply mode to the power supply in the third supply mode, characterized in that the power supply circuit includes a power conversion circuit, the power conversion circuit generates heat, and the photosensitive drum is configured to be warmed by the heat generated by the power conversion circuit. a heating rotating body for heating a paper sheet with the toner image transferred; a heater for heating the heating rotating body; a controller (1, 5) including a control circuit (11, 51); and a power supply circuit for turning on and off power supply to the heater and the controller (1, 5), configured to supply power in one of a first supply mode, a second supply mode, and a third supply mode, the first supply mode being a mode for supplying power so that printing can be performed, and more power being supplied in the first supply mode than in the second supply mode or the third supply mode, more power being supplied in the second supply mode than in the third supply mode, the power supply circuit being configured to switch, in a period other than a predetermined specified period, from the power supply in the first supply mode to the power supply in the second supply mode when a predetermined first transition condition is satisfied, and to switch from the power supply in the second supply mode to the power supply in the third supply mode when a predetermined second transition condition is satisfied, and the power supply circuit being configured to switch, in the specified period, from the power supply in the first supply mode to the power supply in the second supply mode when the first transition condition is satisfied, and to maintain the second supply mode without performing the switching from the power supply in the second supply mode to the power supply in the third supply mode, characterized in that the power supply circuit includes a power conversion circuit, the power conversion circuit generates heat, and the photosensitive drum is configured to be warmed by the heat generated by the power conversion circuit.