PURPOSE: To obtain an apparatus for measuring the inner temperature accurately even for high temperature sample.

CONSTITUTION: When a sample 10 is irradiated with laser light from a laser light source 11 for generating ultrasonic wave, an ultrasonic wave is generated in the sample 10. An ultrasonic detecting section 20 detects an echo of the ultrasonic wave as a Doppler shift of laser light emitted from a laser light source 12 for probe thus determining the propagation time of ultrasonic wave. The propagation time depends on the inner temperature. On the other hand, a surface temperature measuring section 30 determines the temperature of scale based on the Raman scattering of laser light emitted from the laser light source 12 for probe. That temperature is regarded as the surface temperature of the sample. When the temperature is locally distributed in the sample 10, the temperature distribution can be approximated by a specific function including unknown parameters. An arithmetic section 40 calculates the unknown parameters based on the measurements and determines the function. Finally, inner temperature of the sample is determined according to the function.