PURPOSE: To make it possible to perform measurement, which is immune to electromagnetically induced noise and has a high S/N ratio, by measuring the rise time of phosphorescent and fluorescent light based on the output signal of a light receiving means, comparing the result with the temperature characteristics of the rise time, which is preset in correspondence with a phosphorescent and fluorescent body, thereby obtaining the temperature.

CONSTITUTION: When a pulse P1 is inputted, exciting light is outputted from a light emitting device 3, and projected on a fluorescent body 2 through an optical fiber 1. Light emitted from the fluorescent body 2 is inputted to a light receiver 5 through a beam splitter 9. After the amplification, the light is inputted to a sample holding circuit 7. A signal detected by the light receiver 5 at every timing pulse P2 is held by the circuit 7, converted into a digital signal by an A/D converter 8, and stored in an RAM11. When the reception of the sampling data is finished, the rise time is computed by a CPU10. The result is compared with the temperature characteristics of the rise time, which is preset in correspondence with the fluorescent body, and the temperature is obtained.