Provided is a reactor that can prevent a temperature sensor from being attached to a wound portion of a coil in a wrong direction. The reactor includes a temperature sensor having a sensor main portion attached to an outer peripheral surface of a wound portion and a wire extending from the sensor main portion. A sensor housing portion houses the sensor main portion. The sensor main portion has a detection surface facing the wound portion and a projecting portion protruding from a back surface of the sensor main portion opposite of the detection surface. The sensor housing portion has a pair of side wall portions opposing respective side surfaces of the sensor main portion. A height of a portion of the sensor main portion that has the projecting portion is larger than a width of that portion and larger than the distance between the side wall portions.