A developing device has a developing roller, a toner feeding roller, a regulating blade, a casing, a film member, a biasing member, and first and second gears. The casing has an inner wall part facing the developing roller between the regulating blade and an image carrying member. The film member is flexible, and can vibrate in a direction approaching or away from the inner wall part. The biasing member applies a tension to the film member in its longitudinal direction. The first and second gears are coupled to a gear train driving the developing roller or the toner feeding roller, and have formed on their circumferential surfaces first and second protrusions vibrating the film member by intermittently making contact with one edge and the other edge of the film member respectively.