An object is to provide a photoelectric conversion element having a side surface with different taper angles by conducting etching of a photoelectric conversion layer step-by-step. A pin photodiode has a high response speed compared with a pn photodiode but has a disadvantage of large dark current. One cause of the dark current is considered to be conduction through an etching residue which is generated in etching and deposited on a side surface of the photoelectric conversion layer. Leakage current of the photoelectric conversion element is reduced by forming a structure in which a side surface has two different tapered shapes, which conventionally has a uniform surface, so that the photoelectric conversion layer has a side surface of a p-layer and a side surface of an n-layer, which are not in the same plane.