In an image-forming apparatus, a temperature sensor is situated in the position where the sensor is insusceptible to steam. The position is, for example, a portion, of a discharge-sensor lever, where a printing material abuts on the discharge-sensor lever. Accordingly, the temperature sensor becomes insusceptible to steam, whereby the image-forming apparatus can more appropriately control the fixing temperature than conventional image-forming apparatuses. In other words, the image-forming apparatus can more reduce the incidence rate of defects, such as increase, due to excess heating, in the amount of hot-offsets and curls, deterioration of loading capacity, and defective fixing due to scarcity of the amount of heat, than the conventional image-forming apparatuses. Moreover, by determining a threshold temperature every time when a printing material passes through a heat-fixing unit, a problem can be alleviated, in which, at the beginning of a series of paper passage, the amount of fluctuation in detected temperature becomes significantly large.