Provided is a technique for manufacturing a photoelectric conversion element using a dense crystalline semiconductor film without a cavity between crystal grains. A method of manufacturing a photoelectric conversion device having a first electrode, a unit cell, and a second electrode over a substrate includes the steps of: forming a plasma region between a first electrode and a second electrode by supplying high-frequency power of 60 MHz or less to the first electrode under a condition where a pressure of a reactive gas in a chamber of a plasma CVD apparatus is set to from 450 Pa to 13332 Pa, and a distance between the first electrode and the second electrode of the plasma CVD apparatus is set to from 1 mm to 20 mm, preferably, 4 mm to 16 mm; forming deposition precursors including a crystalline semiconductor in a gas phase including the plasma region; forming a crystal nucleus having a grain size of from 5 nm to 15 nm by depositing the deposition precursors; and forming a semiconductor film having a first conductivity type, a semiconductor film effective in photoelectric conversion, or a semiconductor film having a first conductivity type in the unit cell, by growing a crystal from the crystal nucleus.