To provide a temperature measuring instrument capable of measuring a temperature of a measured object, using a microwave.

This temperature measuring instrument for measuring the temperature, based on a propagation path difference between the first reflected wave M1 reflected from a surface and the second reflected wave M2 reflected from a reverse face, by irradiating the measured object W with a measuring wave, is provided with a divider 50 for dividing the microwave into a measuring wave S1 and a reference wave R1, a directional coupler 52 for inputting the measuring wave, an antenna part 44 for the measuring wave, a phase shifter 54 for outputting the reference wave while changing a phase thereof, a coupler 56 for coupling an interference wave of the first and second reflected waves with the phase changed reference wave from the phase shifter to form an interference wave, an electric power detecting part for detecting an output therefrom, and a temperature computing part 60 having preliminarily a reference value of the propagation path difference with respect to the temperature, and for finding the temperature of the measured object, based on a detection result in the electric power detecting part.