Abstract: A developing device includes a developer holding member that holds a developer, a supplying member that supplies the developer to the developer holding member, a transport member that transports the developer while passing the developer onto the supplying member through a passing member, the transport member including a discharge unit that discharges excess developer and that is provided downstream of the passing member in a transport direction, a detecting unit that is provided upstream of the discharge unit in the transport direction and that detects a toner concentration, and a retaining member that includes a non-application portion that prevents action of a force for transporting the developer radially outward and that retains the developer in a region corresponding to the detecting unit of the transport member.

Abstract: A developing device includes a housing that includes an accommodating chamber, a development opening, and a discharge opening, part of developer that is accommodated in the accommodating chamber overflowing into and being discharged from the discharge opening; a developing roller that holds and transports the developer that is supplied from the accommodating chamber; a transporting member that transports the developer in the accommodating chamber so as to supply the developer to the developing roller while stirring the developer; a regulating member that regulates a thickness of a layer of the developer that is held by the developing roller by holding back part of the developer; and a ventilation path portion that is provided so as to extend through the regulating member, the ventilation path portion being connected to a gap space that exists in a range extending to the development opening from where the developing roller passes the regulating member.

Abstract: A developing device includes a developer holding member that holds a developer, a supplying member that supplies the developer to the developer holding member, a transport member that transports the developer while passing the developer onto the supplying member through a passing member, the transport member including a discharge unit that discharges excess developer and that is provided downstream of the passing member in a transport direction, a detecting unit that is provided upstream of the discharge unit in the transport direction and that detects a toner concentration, and a retaining member that includes a non-application portion that prevents action of a force for transporting the developer radially outward and that retains the developer in a region corresponding to the detecting unit of the transport member.

Abstract: A developing device includes a housing that includes an accommodating chamber, a development opening, and a discharge opening, part of developer that is accommodated in the accommodating chamber overflowing into and being discharged from the discharge opening; a developing roller that holds and transports the developer that is supplied from the accommodating chamber; a transporting member that transports the developer in the accommodating chamber so as to supply the developer to the developing roller while stirring the developer; a regulating member that regulates a thickness of a layer of the developer that is held by the developing roller by holding back part of the developer; and a ventilation path portion that is provided so as to extend through the regulating member, the ventilation path portion being connected to a gap space that exists in a range extending to the development opening from where the developing roller passes the regulating member.

Abstract: A developing method for an image formation system includes the steps of supplying a toner and developing an electrostatic latent image formed on a latent image support of the image formation system with the toner for visualization. A toner amount of a solid area T(g/m.sup.2) has a maximum toner amount per unit area on a recording medium and satisfies the following expression:1.ltoreq.T/a.ltoreq.1.2wherein a=(4.pi./3).multidot.(dt/2).sup.3 .multidot..rho.t({(3).sup.1/2 .multidot.dt.sup.2 /2} (g/m.sup.2), where dt is a toner volume center diameter (m) and st is a toner density (g/m.sup.3). A developing device for developing an electrostatic latent image includes toner amount regulation means for regulating a toner amount that satisfies the above expression.