A p− type semiconductor substrate 20 has a first principal surface 20a and a second principal surface 20b opposed to each other and includes a photosensitive region 21. The photosensitive region 21 is composed of an n+ type impurity region 23, a p+ type impurity region 25, and a region to be depleted with application of a bias voltage in the p− type semiconductor substrate 20. An irregular asperity 10 is formed in the second principal surface 20b of the p− type semiconductor substrate 20. An accumulation layer 37 is formed on the second principal surface 20b side of the p− type semiconductor substrate 20 and a region in the accumulation layer 37 opposed to the photosensitive region 21 is optically exposed.