PURPOSE: To suppress and take a measurement to thermal vibration easily and accurately by measuring the thermal distribution of a body of revolution without contacting by photodetecting a light signal, modulated on the surface of the body revolution corresponding to temperature, by a measurement processing part via an optical fiber.

CONSTITUTION: A multiplexed light beam from measurement processing part 6 is sent to the surface of rotator 1 in rotation via optical fiber 4. The surface of rotator 1 is applied with a heat-sensitive coating material which changes in light and shade corresponding to temperature. Then, this light beam is returned to photosensor 2 as a light signal modulated corresponding to the surface temperature of the body of revolution and then sent back to measurement processing part 6 via optical fiber 4. Meansurement processing part 6 demodulates the light signal to obtain the surface temperature of rotator 1. Thus, the surface temperature distribution of rotator 1 is accurately measured to detect easily and securely the cause of the occurrence of vibration due to thermal unbalance, so that an adequate counter measure to it can be taken.