A lens allows infrared light to pass therethrough. An infrared sensor includes infrared detection elements arranged in two or more columns. The infrared sensor is rotated around a scan rotation axis that passes through part of the lens to scan a detection range, and outputs an output signal indicating a thermal image of the detection range. At least two infrared detection elements in the infrared sensor are located at positions displaced from each other with respect to the scan rotation axis. Among the infrared detection elements, the number of first infrared detection elements having a smaller half-width of a point spread function in a scan direction than that in the direction of the scan rotation axis is larger than the number of second infrared detection elements having a larger half-width of a point spread function in the scan direction than that in the direction of the scan rotation axis.