The present invention provides an image reading device, an image printing system and image forming device in which variation in light intensity caused by the continuous lighting time of an exposure lamp serving as a light source for reading an original is prevented, a read image is prevented from deteriorating and wasteful power consumption is prevented. The exposure lamp is turned off after a predetermined time has passed from a time when the original finishes passing through a reading position or the original is conveyed to a standby position. Alternatively, the exposure lamp is turned off without setting the predetermined time in a group-copy mode.