A dual pyroelectric sensor including two pyroelectric elements (91R, 91L), the two pyroelectric elements (91R, 91L) being connected in series with reverse polarity and being disposed point-symmetric with respect to a center of the dual pyroelectric sensor on a sensing surface, the dual pyroelectric sensor comprising a mask applied to the sensing surface of the dual pyroelectric sensor to increase sensitivity with which the pyroelectric sensor detects a moving object, the mask comprising: a sheet configured to block infrared rays; and an aperture pattern comprising a plurality of through holes (112.1-112.8) formed in the sheet, wherein the aperture pattern is asymmetric with respect to a x-direction axis passing through the center of the pyroelectric sensor, and the aperture pattern is asymmetric with respect to a y-direction axis passing through the center of the pyroelectric sensor, the x-direction being a disposition direction of the two pyroelectric elements (91R, 91L) on the sensing surface, the y-direction being a direction perpendicular to the x-direction on the sensing surface, wherein the sheet comprises a first portion parallel with the y-direction axis passing through the center of the pyroelectric sensor and a second portion disposed on the periphery of the mask, wherein the aperture pattern comprises a first aperture region and a second aperture region surrounded by the first and second portions and each one of the aperture regions being disposed on a different side of the y-direction axis, wherein an edge in the y-direction, of the first aperture regions protrudes further in the y-direction than an edge in the y-direction, of the second aperture region, and whereby the percentages of the respective irradiated ranges of the pyroelectric elements (91R, 91L) vary with a movement of a moving object in each of the x- and y-directions. a sheet configured to block infrared rays; and an aperture pattern comprising a plurality of through holes (112.1-112.8) formed in the sheet, wherein the aperture pattern is asymmetric with respect to a x-direction axis passing through the center of the pyroelectric sensor, and the aperture pattern is asymmetric with respect to a y-direction axis passing through the center of the pyroelectric sensor, the x-direction being a disposition direction of the two pyroelectric elements (91R, 91L) on the sensing surface, the y-direction being a direction perpendicular to the x-direction on the sensing surface, wherein the sheet comprises a first portion parallel with the y-direction axis passing through the center of the pyroelectric sensor and a second portion disposed on the periphery of the mask, wherein the aperture pattern comprises a first aperture region and a second aperture region surrounded by the first and second portions and each one of the aperture regions being disposed on a different side of the y-direction axis, wherein an edge in the y-direction, of the first aperture regions protrudes further in the y-direction than an edge in the y-direction, of the second aperture region, and whereby the percentages of the respective irradiated ranges of the pyroelectric elements (91R, 91L) vary with a movement of a moving object in each of the x- and y-directions.