PURPOSE: To make it possible to sense the heated material having a broad temperature range by one sensor assuredly, by incorporating an amplifier, wherein the gain is automatically adjusted in response to the temperature of the heated material, into the heated material sensing device utilizing infrared ray.

CONSTITUTION: The infrared ray irradiated from the heated material is converted into the electrical signal. Said signal is amplified by the amplifier wherein the gain is automatically adjusted in rsponse to the temperature of the heated material. When said electrical signal has reached a specified value, an output relay is actuated, and the sensing of the heated material is performed. For example, the infrared ray from the heated material 1 is received by a light receiving element 3 which is provided in a control chamber 19 through a lens 2 and optical fiber 9, and amplified by the amplifier 4. In the case the output exceeds a specified value, the output relay 6 is actuated through a Schmitt trigger 5, and the sensing of the heated material is performed. In this case, a switch 10 is actuated by an input 11 which is varied by the temperature of the heated material, and the gain of the amplifier is automatically adjusted. Thus the secure sensing can be performed.