To provide an infrared sensor capable of preventing a sensor element from breaking due to heat when the sensor element having a membrane is directly mounted to a circuit board to achieve compactness.

In the sensor element 30, a membrane part 32 is formed by forming a recessed part 31 for one surface side of the sensor element 30, and a thick wall part 33 is provided for a peripheral part of the membrane part 32. The sensor element 30 is fixed to one surface side of the circuit board 20 at the thick wall part 33 on the one surface side of the sensor element 30 via an adhesive 40. A gap part 50, an area not provided with the adhesive 40, is formed between the thick wall part 33 on the one surface side of the sensor element 30 and the one surface side of the circuit board 20, and the space inside the recessed part 31 communicates with the outside via the gap part 50.