MIRROR SURFACE COOLING TYPE SENSOR

PROBLEM TO BE SOLVED: To balance price and performance of a main controller and a sub controller, thereby reducing a price of a product.SOLUTION: On one end of a heat conductor 17 (a sensor body 13, a cooling block 15, a cooling plate 16), there is attached an electrothermal cooling element (first electrothermal cooling element) 2 for mirror surface cooling. On the other end of the heat conductor 17, there is attached, as an auxiliary cooler, an electrothermal cooling element (second electrothermal cooling element) 18 having a large cooling capacity. A supply current to the first electrothermal cooling element 2 is controlled by a main controller 24, and a supply current to the second electrothermal cooling element 18 is controlled by a sub controller 25. In this configuration, a controller with high performance and a high price is employed for the main controller 24, and a controller with low performance and a low price is employed for the sub controller 25. Particularly, the main controller 24 is more accurate in A/D conversion and has a shorter control period than the sub controller 25.