This invention suppresses power consumption in an image forming apparatus using an electron-emitting device. For this purpose, an image forming apparatus has a plurality of electron-emitting devices, a light-emitting substance for emitting light by irradiation of electrons emitted by the electron-emitting devices, a first potential application means for sequentially selecting the plurality of electron-emitting devices and applying, to a selected electron-emitting device, a predetermined potential different from a potential applied to an unselected electron-emitting device, and a second potential application means for applying a potential corresponding to an image signal to at least a selected electron-emitting device. In this image forming apparatus, when the light-emitting substance is not required to emit light by irradiation of electrons from the selected electron-emitting device, a voltage applied to the selected electron-emitting device is set around the threshold of emission/non-emission of the light-emitting substance by irradiation of electrons from the electron-emitting device.