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.