A developing device comprising: a developing container capable of accommodating a developer (t); a developing roller , disposed at an opening of said developing container , for developing an electrostatic latent image formed on an image bearing member with the developer (t) carried thereon; a developer supplying roller , disposed inside said developing container , for supplying the developer (t) to said developing roller in contact with said developing roller ; a sheet member , which is attached to said developing container at its base end portion and which contacts said developing roller at its free end portion, for preventing the developer (t) from leaking out of said developer container ; a communication hole , provided in a wall of said developing container , for establishing communication between an inside and an outside of said developing container ; and a filter member for covering said communication hole so as to prevent passage of the developer (t) therethrough while permitting passage of air therethrough, wherein said communication hole is provided so as to be connected to an enclosed space (J) defined by an inner wall of said developing container defining a smaller one of spaces provided by dividing said developing container by a plane (U) including a rotation axis (8a4) of said developer supplying roller and a rotational axis (2a4) of said developing roller , a phantom plane which is included in the plane (U) and extends from a surface (8a3) of said developer supplying roller to the inner wall of said developer container , said sheet member , a surface (2a3) of said developing roller , and said surface (8a3) of said developer supplying roller , characterized in that the filter member is fixed on the communication hole so as to cover the communication hole from the outside of the developing container . a developing container capable of accommodating a developer (t); a developing roller , disposed at an opening of said developing container , for developing an electrostatic latent image formed on an image bearing member with the developer (t) carried thereon; a developer supplying roller , disposed inside said developing container , for supplying the developer (t) to said developing roller in contact with said developing roller ; a sheet member , which is attached to said developing container at its base end portion and which contacts said developing roller at its free end portion, for preventing the developer (t) from leaking out of said developer container ; a communication hole , provided in a wall of said developing container , for establishing communication between an inside and an outside of said developing container ; and a filter member for covering said communication hole so as to prevent passage of the developer (t) therethrough while permitting passage of air therethrough, wherein said communication hole is provided so as to be connected to an enclosed space (J) defined by an inner wall of said developing container defining a smaller one of spaces provided by dividing said developing container by a plane (U) including a rotation axis (8a4) of said developer supplying roller and a rotational axis (2a4) of said developing roller , a phantom plane which is included in the plane (U) and extends from a surface (8a3) of said developer supplying roller to the inner wall of said developer container , said sheet member , a surface (2a3) of said developing roller , and said surface (8a3) of said developer supplying roller , characterized in that the filter member is fixed on the communication hole so as to cover the communication hole from the outside of the developing container . <EOS>