A human body detecting device comprising: a pyroelectric element; a lens array having a plurality of lenses collecting infrared rays to the pyroelectric element; and a determination device outputting a human body detection signal based on an output signal of the pyroelectric element, wherein the pyroelectric element includes a plurality of detecting units each having a front-side electrode and a back-side electrode, wherein the pyroelectric element includes a first detecting unit with polarity of the front-side electrode positive and a second detecting unit with polarity of the front-side electrode negative, as the plurality of detecting units, wherein a plurality of infrared ray reception paths is defined by one lens and the plurality of detecting units in one-to-one correspondence to the plurality of detecting units for each of the plurality of lenses, wherein the plurality of infrared ray reception paths includes a plurality of first infrared ray reception paths defined by any one of the plurality of lenses and the plurality of detecting units; and a plurality of second infrared ray reception paths defined by one lens adjacent to the any one of the plurality of lenses and the plurality of detecting units, wherein the lens array is configured so that a view, on a plane, that the pyroelectric element views through a lens corresponding to one of the plurality of first infrared ray reception paths and a view, on the plane, the pyroelectric element views through a lens corresponding to one of the plurality of second infrared ray reception paths overlap with each other, and wherein the front-side electrodes of two detecting units respectively corresponding to the one first infrared ray reception path and the one second infrared ray reception path overlapping with each other, of the plurality of detecting units have same polarity, characterized in that the lens array is configured so that part of the one first infrared ray reception path and part of the one second infrared ray reception path overlap with each other, wherein the shape of the infrared ray reception path on a virtual plane is a diamond with its two diagonal lines different in length from each other, wherein a distance from the human body detecting device to the virtual plane is the maximum detection distance or smaller than the maximum detection distance. a pyroelectric element; a lens array having a plurality of lenses collecting infrared rays to the pyroelectric element; and a determination device outputting a human body detection signal based on an output signal of the pyroelectric element, wherein the pyroelectric element includes a plurality of detecting units each having a front-side electrode and a back-side electrode, wherein the pyroelectric element includes a first detecting unit with polarity of the front-side electrode positive and a second detecting unit with polarity of the front-side electrode negative, as the plurality of detecting units, wherein a plurality of infrared ray reception paths is defined by one lens and the plurality of detecting units in one-to-one correspondence to the plurality of detecting units for each of the plurality of lenses, wherein the plurality of infrared ray reception paths includes a plurality of first infrared ray reception paths defined by any one of the plurality of lenses and the plurality of detecting units; and a plurality of second infrared ray reception paths defined by one lens adjacent to the any one of the plurality of lenses and the plurality of detecting units, wherein the lens array is configured so that a view, on a plane, that the pyroelectric element views through a lens corresponding to one of the plurality of first infrared ray reception paths and a view, on the plane, the pyroelectric element views through a lens corresponding to one of the plurality of second infrared ray reception paths overlap with each other, and wherein the front-side electrodes of two detecting units respectively corresponding to the one first infrared ray reception path and the one second infrared ray reception path overlapping with each other, of the plurality of detecting units have same polarity, characterized in that the lens array is configured so that part of the one first infrared ray reception path and part of the one second infrared ray reception path overlap with each other, wherein the shape of the infrared ray reception path on a virtual plane is a diamond with its two diagonal lines different in length from each other, wherein a distance from the human body detecting device to the virtual plane is the maximum detection distance or smaller than the maximum detection distance.