In an infrared sensor 1 including a condenser lens 3 and a multi-element light-receiving unit 2 with a plurality of light-receiving elements 2a to 2h aligned therein on a straight line, a position of receiving an intensity distribution peak of infrared rays which have passed through the condenser lens 3 is deviated from the center position of the multi-element light-receiving unit 2 to a desired light-receiving element position. Especially when the infrared sensor 1 is included in an air conditioner, the position of receiving the intensity distribution peak of the infrared rays is set to the position of a light-receiving element used for detecting heat in a location far from the installment position of the air conditioner.