A pyroelectric detector comprising a functional portion in which opposed electrodes 111 to 118 are formed on both surfaces of a pyroelectric type substrate 101 and four light receiving electrode portions a, b, c and d are structured by the opposed electrodes 111 to 118. Among the light receiving electrode portions a, b, c and d, the light receiving electrode portions a and c in odd-numbered positions constitute one light receiving electrode group A and the light receiving electrode portions b and d in even-numbered positions constitute the other light receiving electrode group B. The light receiving electrode portions a and c and the light receiving electrode portions b and d are electrically connected alternately and in series, and the light receiving electrode group A and the other light receiving electrode group B are connected to have opposite polarities.