Disclosed is a photodiode having a silicon film (5) formed of a continuous grain silicon, where the silicon film (5) has a p-type semiconductor region (2), an intrinsic semiconductor region (3) and an n-type semiconductor region (4), which are arranged in this order along the surface of the silicon film (5). The intrinsic semiconductor region (3) is formed to be in contact with the p-type semiconductor region (2) and the n-type semiconductor region (4). The distance L from the boundary between the intrinsic semiconductor region (3) and the p-type semiconductor region (2) to the boundary between the intrinsic semiconductor region (3) and the n-type semiconductor region (4) is set to not less than 2.5 μm and not more than 10 μm. The distance L is preferably set to not less than 3 μm and not more than 7 μm.