A thermistor is disposed confronting a surface of a heat roller on a
downstream side in a rotational direction of a heat roller from a contact
position between the heat roller and a pressure roller. Side guide
members are provided on both sides of the thermistor and spaced away from
the thermistor in the axial direction of the heat roller, and a
regulating guide member is disposed connecting the side guide members on
the downstream side in the rotational direction of the heat roller. In
addition, a separation plate for separating a sheet of paper is provided
at a predetermined space from the surface of the heat roller between the
contact position and the thermistor in the rotational direction.