To achieve higher definition of a channel portion of an organic transistor and to reduce bulging at the edge part of the channel portion. A manufacturing method of an organic transistor includes: forming a gate electrode on a substrate surface; forming a gate insulating film on the substrate surface to cover the gate electrode; forming a drain electrode and a source electrode with a predetermined distance therebetween on the gate insulating film surface and at a position where each electrode partially overlaps with the gate electrode; forming a liquid crystal alignment film on the gate insulating film surface to cover the drain electrode and the source electrode; forming an opening part by dripping an etchant to a region of the liquid crystal alignment film that overlaps with the gate electrode in a plane view; and forming an organic semiconductor film at the opening part of the liquid crystal alignment film.