PURPOSE: To obtain temperature distribution at a high speed, by imparting heat change to an object at the specified time before the image spot of an infrared ray detector passes a measuring point, and taking out an infrared ray image signal as a data when the spot of the infrared ray detector passes the measuring point.

CONSTITUTION: The image spot of the infrared ray detector 1 is formed on the subject 3 by a light scanner 2. The infrared rays irradiated from the point, where the spot image is formed, are detected by the detector 1 and sent to a CRT8 as a luminance signal. An oscillator 14 generates a clock signal corresponding to picture elements. The counted value from a counter 15 indicates the position of the image spot. The image signal of the first picture element is sent to the CRT8. The image signal of the second picture element is sent to the CRT8 when the second horizontal scanning is performed at the same position. At the specified time before the data is taken out, the object 3 (transistor) is switched and the heat change is imparted thereto.