To prevent a sealing member from breaking away from a device body even when the sealing member is bent.

A toner replenishing type developing device 4Y, 4M, 4C or 4B comprises a developing device body 4a, and a sealing member 4e. The sealing member 4e comprises an insertion and removal part 41a which a toner replenishing pipe 13Y, 13M, 13C, or 13B is inserted into and removed from, and a bending part 41b which bends by the insertion of the replenishing pipe 13Y, 13M, 13C or 13B into the insertion and removal part 41a, and is restored to its original state by the removal of the toner replenishing pipe 13Y, 13M, 13C or 13B from the insertion and removal part 41a. The bending part 41b of the sealing member 4e is formed in such a manner that the thickness t2 thereof in the insertion direction of the toner replenishing pipe 13Y, 13M, 13C or 13B at the bending part 41b is smaller than the thickness t1 of the insertion and removal part 41a in the insertion direction of the toner replenishing pipe 13Y, 13M, 13C or 13B at the insertion and removal part 41a.