A developing apparatus is provided that can reliably prevent a developer from leaking even where the developing apparatus is continuously used, and an image forming apparatus having the developing apparatus is provided. The developing apparatus has a developer container for containing a developer, a developing portion for generating a developer image by developing an electrostatic latent image formed on an electrostatic latent image holder using the developer contained in the developer container, a seal member formed along a surface of an end portion of the developing portion for sealing between the developer container and the developing portion, and a supporting member for supporting the seal member so as to allow displacement.