1. A defect inspection apparatus comprising: illumination unit for illuminating an inspection target with illumination light; a detector that has photoelectric image sensors to receive light reflected from the inspection target; a transport unit for transporting the detector or a stage on which the inspection target is mounted; and an inspection unit for inspecting the inspection target in accordance with an image detected by the detector, wherein the plurality of photoelectric image sensors are alternately arranged in each of two or more lines to form a lattice-like pattern, and the plurality of photoelectric image sensors are spaced apart from each other to provide a mounting space, and at least one of a sensor cooling mechanism, a driver circuit, and an electron multiplier is arranged in said mounting space.