An image forming apparatus orientatable in either a first position or a second position, the second position being different from the first position in inclination with respect to a horizontal plane, comprising: a fixing device including a heating roller and a pressurizing member, pressing the pressurizing member against a surface of the heating roller to form a fixing nip, and thermally fixing a toner image on a recording sheet passing through the fixing nip; at least one temperature detector detecting surface temperature of the heating roller without contact with the surface; a heater heating the heating roller; a controller controlling the heater according to the surface temperature, thereby controlling the surface temperature; and a switcher switching a detection point of the temperature detector between a first and a second detection point according to whether the image forming apparatus is in the first or the second position.