An image forming apparatus includes an image forming unit configured to form an image on a sheet in accordance with inputted image data, an opening portion configured to allow airflow between an inside and an outside of the image forming apparatus, a detector disposed adjacent to the opening portion and configured to detect a temperature, a fan configured to suction air through the opening and to discharge air from the inside of the image forming unit to cool the image forming unit, a controller configured to control a rotational speed of the fan so as to rotate the fan at a first rotational speed, in an initial state of the image forming apparatus, after actuation of the image forming apparatus, and to rotate the fan at a second rotational speed, less than the first rotational speed, in a stand-by state waiting for the image data to be input after the initial state, and a setting portion configured to set an image forming condition of the image forming unit on the basis of an output of the detector acquired as a result of rotation of the fan at the first rotational speed.