An internal temperature measuring apparatus includes a base and a MEMS device disposed on the base. The MEMS device includes a top face and a support. The top face includes a first thermopile configured to measure a first temperature difference used to calculate an internal temperature and a second thermopile configured to measure a second temperature difference used to calculate the internal temperature together with the first temperature difference. An orientation in which a cold junction of each thermocouple constituting the first thermopile is viewed from a hot junction coincides with an orientation in which a cold junction of each thermocouple constituting the second thermopile is viewed from a hot junction.