In a pyroelectric infrared detector, there is provided a slit which interrupts an infrared image which is incident to a pyroelectric element array, and respec­tive pyroelectric elements forming one row of the pyroelectric element array are wired so that they are connected in series electrically and adjacent pyroelectric elements generate counter-electromotive forces. An infrared image irradiated on respective pyroelectric elements is scanned successively by the movement of the slit in a row direction on the pyroelectric element array, thus obtaining an infrared image which is being irradiated onto respective pyroelectric elements from time series signals produced at both ends of the pyroelectric element array.