PURPOSE: To prevent malfunction to be caused by heat transmitted to a pyroelectric element from a support board and lowering of sensitivity of a pyroelectric detection part by sticking the lower face of a center part between two pyroelectric detection parts of the pyroelectric element on the upper face of a projection part provided on the support board.

CONSTITUTION: Heat applied to one side of a support board 2 is transmitted to a pyroelectric element 1 through a projection part 2a. At this time, because the projection part 2a is stuck on the center part between two pyroelectric detection parts 11, 1b, heat transmission facility is equalized in the two pyroelectric detection parts 11, 1b, which are not mutually unbalanced. Therefor, malfunction does not occur. In addition, the heat applied to one detection part 1a is transmitted to the other detection part 1b through the element l and it is difficult to transmit the heat because it is transmitted from the center part of the two detection parts 1a, 1b to the projection part 2a. Accordingly lowering of sensitivity can be prevented.