A laser printer capable of controlling the operation of a fixing heater to heat a roller, including an energizing circuit for energizing a heater, a temperature detecting circuit such as thermistors, a noise canceling circuit, and a control circuit for controlling the energizing circuit and the heater. After receiving a voltage indicating an abnormal temperature of the heater over a prescribed length of time duration, the noise canceling circuit is configured to transmit a LOW level voltage to a latch circuit as an abnormality signal. The control circuit suspends the energization of the heater in response to the abnormality signal.