To provide at low cost a structure capable of measuring the temperature of a road surface partially and with practically sufficient accuracy.

An optical fiber 3 is laid near the surface of a road 1 and the temperature of a predetermined portion of the road surface is detected using the Raman effect. Electric heaters 5a to 5d for heating the road surface are provided in series in the direction in which the optical fiber 3 is laid, in such a way that the heaters can be powered independently of one another. Either of the heaters is powered to raise the temperature of a portion of the optical fiber 3 to initialize an optical-fiber thermometer 4. Because no special temperature regulating means is needed for the initialization, the structure can be provided at low cost.