To provide a temperature measuring device capable of accurately measuring a temperature of a temperature measuring object in a noncontact state from the temperature measuring object without being influenced by transmissivity of the light of a transmission body.

This temperature measuring device has a temperature-known standard black body furnace 17 on the outside of a vacuum chamber 10, and a reflecting mirror 16 on the inside of the vacuum chamber 10. The emitted light emitted from the standard black body furnace 17 is made incident on a radiation thermometer 15 via a transmission window 14, the reflecting mirror 16, and the transmission window 14 in this order, and a temperature of the standard black body furnace 17 is measured. Thus, a temperature error in a GaAs base board 11 when the emitted light from the GaAs base board 11 passes through the transmission window 14 can be determined on the basis of an actual temperature of the standard black body furnace 17 and the temperature of the standard black body furnace 17 measured by the radiation thermometer 15 so that a surface temperature of the GaAs base board 11 can be accurately determined.