A developing device includes an agitating member, a magnetic roller, a lower housing, an upper housing and a blade member. The lower housing includes a first housing part including a first edge having a first contact face and a first facing surface at a blade member's side. The upper housing includes a second housing part including a second edge having a second contact face contact with the first contact face and a second facing surface facing to the first facing surface. The blade member is attached to the upper housing and arranged at a gap to the lower housing. Between the first and second facing surfaces, a width at a blade member's side is broader than a width at a first contact face's side. The first and second facing surfaces are bonded by an adhesive agent. The gap is sealed by the adhesive agent.