The present invention addresses the problem of providing an infrared detection device with which detection of a heat source passing across a detection area can be suppressed. An infrared detection device (10) comprises a pyroelectric element and an optical system. The optical system includes a plurality of lenses arranged in a row, and focuses infrared rays at the pyroelectric element. A detection area (11) which is determined by a light reception unit including the pyroelectric element and the optical system includes a plurality of small detection areas (12) corresponding one-on-one to the plurality of lenses. The optical system is configured such that the sensitivity of the pyroelectric element when a heat source (200) to be detected moves in a direction along a first direction (D1) intersecting the plurality of small detection areas (12) becomes smaller than the sensitivity of the pyroelectric element when the heat source (200) moves in a direction along a second direction (D2) along the optical axis of at least one of the plurality of lenses.