PURPOSE: To provide a temperature controller of a simple constitution which can control the temperature with high accuracy and high stability without receiving any effect of the voltage variance of an AC power supply and regardless of the dimentional accuracy of the heat-sensitive layer of a temperature measuring element and furthermore can stop the energization of a heater when the temperature measuring element and the parts have the faults.

CONSTITUTION: The voltage of an AC power supply 1 is divided and applied to a transistor TR 7, and the phase difference between the AC voltage applied to a temperature measuring element and the current flowing to this element is calculated as the output of the TR 7 in each cycle of the power supply 1. Then, the output of the TR 7 is used as a temperature measuring signal and a temperature control means of the following stage controls the temperature of a heater regardless of the voltage variance of the power supply 1.