To provide a pyroelectric sensor element which has small heat capacity, high sensitivity, and high responsiveness, which is difficult to cause dielectric breakdown at polarization, and which allows mass production while achieving size reduction and cost reduction.

A pyroelectric sensor element comprises a substrate 2, a pyroelectric thin film 4 formed on the substrate 2, and an upper electrode 3 disposed on the pyroelectric thin film 4. The upper electrode 3 includes two electrode pairs 3a and 3b disposed to face each other, and signal extraction electrodes 3c and 3d, thereby forming a comb-like electrode. By applying voltage between the signal extraction electrodes 3c and 3d, the pyroelectric thin film 4 is polarized in an in-plane direction of the film between the electrode pair 3a and the electrode pair 3b facing each other, and between the electrode pairs 3a and 3b. No conductor is present in the vicinity of a lower surface of a region 6 where the electrode pairs 3a and 3b of the pyroelectric thin film 4 exist. The substrate 2 is a silicon substrate, and the substrate 2 is entirely removed in a lower part region 7 of the region 6 where the electrode pairs 3a and 3b of the pyroelectric thin film 4 exist.