An image forming apparatus includes an image forming unit, a heater, a heat receiving member configured to fix a toner image on a sheet, a first temperature sensor configured to sense a first temperature of the heat receiving member, a second temperature sensor configured to sense a second temperature of the heat receiving member, and a controller. The controller is configured to, after the image forming unit starts image formation: when a difference between the first temperature and the second temperature exceeds a threshold value a first number of times, perform a temperature reduction control in which the controller reduces a number of sheets to be printed per unit time and the image forming unit performs image formation for the reduced number of sheets to be printed per unit time; and increase the threshold value in accordance with a time elapsed.