The service life of electrical equipment is predicted using a thermal history sensor mounted in the electrical equipment. At least one thermal history sensor is mounted inside or on an outer wall surface of electrical equipment. The thermal history sensor includes dissimilar metal joints, and the resistance values of the dissimilar metal joints change in response to the amount of intermetallic compound growing in the dissimilar metal joints due to the temperature inside the electrical equipment or of the outer wall thereof during operation. A determining mechanism periodically or irregularly monitors and stores in memory the resistance values of the dissimilar metal joints from the thermal history sensor, and uses the stored history of resistance values to predict the service life of the electrical equipment.