To switch thereby enabling usage with a wide angle of view and with a high angle resolution according to need by forming an entrance aperture to a light-shielding cover set at a main body to which a plurality of temperature sensors are fixed and which has a solar light introduction space, and introducing a solar light to the temperature sensors.

The interior of a cylindrical part 2b of a main body 2 is a solar light introduction space. Many temperature sensors 3 are embedded in a sensor mount face 2a to detect a temperature rise by a sun light entering from an entrance aperture 5. A light-shielding cover 4 is shaped like a cylinder with one end closed by an end face 4a and arranged to cover the cylindrical part 2b and an open end of the main body 2. The entrance aperture 5 is formed approximately at the center of the end face 4a. The light-shielding cover 45 is made relatively movable to the main body 2 by rotating a pinion 6 by a driving mechanism. A distance from the temperature sensor 3 detecting the solar light to the entrance aperture 5 via the solar light introduction space is changeable, and therefore a wide angle of view and a high angle resolution can be switched according to need.