A fixing unit includes a heater, a fixing member, a press roller, a sensor, a processor, and a memory. The fixing member is heated by heat generated by the heater. The press roller forms a nip portion through which a medium having a fixing target material transferred thereto passes, between the press roller and the fixing member. The sensor measures a temperature of the fixing member. The processor controls the temperature of the fixing member so as to be a target value by acquiring the temperature detected by the sensor in a first period, and also acquires the temperature detected by the sensor in a second period shorter than the first period. The memory records the temperature acquired in the second period.