An apparatus is disclosed which is for forming an image using a fuser unit, including: a fuser roller; a heater heating the fuser roller; a temperature sensor detecting a temperature of the fuser roller; and a controller controlling the heater to substantially achieve a desired temperature of the fuser roller, wherein the controller includes a desired-temperature setting device. The device is operated during a cold start of the fuser unit, so as to set the desired temperature to a second standby-temperature which is lower than a fusing temperature and higher than a normal standby-temperature, so as to maintain the desired temperature at the second standby-temperature during a heat-storing period during which heat is stored in the fuser unit, and so as to set the desired temperature to the normal standby-temperature upon termination of the heat-storing period.