A temperature regulating apparatus which regulates temperature includes a heater, a temperature detector configured to detect temperature, a calculator configured to calculate a manipulated value based on an error between a target temperature and the temperature detected by the temperature detector, and a power controller configured to supply power, having one of a voltage and current controlled in accordance with the manipulated value, to the heater. The calculator includes a first calculator having at least a proportional element of the proportional element, an integral element, and a derivative element, and a second calculator configured to calculate a square root. The first calculator and the second calculator are coupled in series with each other.