STRUCTURE FOR MASKS

Provided is a mask used in a dual pyroelectric sensor and configured to allow the pyroelectric sensor to accurately detect a movement of a moving object in each of the disposition direction of two pyroelectric elements and a direction perpendicular to the disposition direction. The mask is applied to the sensing surface of the dual pyroelectric sensor to increase the sensitivity with which the pyroelectric sensor detects the moving object. The mask includes a sheet configured to block infrared rays and an aperture pattern including through holes formed in the sheet. The aperture pattern is formed in such a manner that the percentages of the respective infrared-irradiated ranges of the two pyroelectric elements of the pyroelectric sensor vary with a movement of a moving object in each of x- and y-directions. The x-direction is the disposition direction of the two pyroelectric elements on the sensing surface, and the y-direction is a direction perpendicular to the x-direction on the sensing surface.