A cryogenic optical detector has been fabricated by using a polycrystalline thin film of an oxide superconductor, BaPb0.7Bi0.3O3(BPB). For a wide detective area, the BPB detector was patterned into a shape of meander line, which consists of a great number of Josephson junction serially connected through the grain boundary. As a result of accumulation effect of Josephson junction arrays, the optical responsivity for the BPB detector with the detection area of 1×1 mm2 is obtained up to about 104 V/W, which is larger than that of InSb hot electron detector in 100 µm wavelength region.