Patent ID: 7899356

Claim:
A developing device comprising: a casing which contains a developing agent and has an opening extending longitudinally thereof; a developing agent carrier rotatably provided in the casing as being exposed from the opening and carrying the developing agent; leak preventing members disposed at longitudinally opposite ends of the opening for preventing the developing agent from leaking out of the casing; and a layer-thickness regulating member kept in pressure contact with a surface of the developing agent carrier for forming a thin layer of the developing agent on the surface of the developing agent carrier, wherein the layer-thickness regulating member includes: a thin plate member having a thin plate shape extending longitudinally of the casing to positions such as to overlap with the leak preventing members, and having a downstream edge portion fixed to the casing with respect to a direction of rotation of the developing agent carrier that is the same direction as a direction perpendicular to a longitudinal direction of the casing and a free upstream edge portion with respect to the rotation direction; and a projection member provided on the free edge portion of the thin plate member as extending longitudinally of the casing and projecting toward the developing agent carrier, wherein the leak preventing members each include a first seal member and a second seal member each disposed along the rotation direction, wherein the first seal member includes: a first downstream portion disposed adjacent, longitudinally of the casing, to the projection member on a front surface of the thin plate member opposed to the developing agent carrier; and a first upstream portion extending upstream of the first downstream portion with respect to the rotation direction continuously from the first downstream portion, wherein the second seal member includes: a second downstream portion disposed on a rear surface of the thin plate member facing away from the developing agent carrier, the second downstream portion being opposed to the first downstream portion and a portion of the projection member adjacent to the first downstream portion with intervention of the thin plate member; and a second upstream portion which extends upstream of the second downstream portion with respect to the rotation direction continuously from the second downstream portion, and integrally includes a covered portion covered with the first upstream portion, an opposed portion disposed adjacent, longitudinally of the casing, to the covered portion and opposed to the projection member in the rotation direction, and an exposed portion extending upstream of the covered portion and the opposed portion with respect to the rotation direction.