To actualize the enhancement of detection accuracy by bringing a window material and a thermopile chip as close as possible to each other to eliminate the effect of infrared radiation independently of changes in environmental temperatures.

A corner part of a rectangular thermopile chip 2 provided on an upper surface of a stem 1 is bonded to an end part of a lead pin 4 on the stem 1 side by means of a bonding wire 5. An opening part 8 is formed in an upper surface part of the thermopile chip 2 corresponding to a light receiving part 6 thereof. The stem 1 is crowned with a downward opening cap 7, with a rectangular window material 9 fitted to an inner surface thereof for blocking the opening part 8. The window material 9 and the thermopile chip 2 are disposed and fixed in a relative positional relation in which they are angularly shifted from each other so that the window material 9 does not overlap with the bonding wire 5 in top plan view, and that the window material 9 overlaps with the bonding wire 5 one above the other in horizontal plan view.