In a structure for removably installing a developing unit inside a case of an electrophotographic image forming apparatus and in an electrophotographic image forming apparatus employing the same, a guide rail is formed at an inner side of the case of the electrophotographic image forming apparatus and it slopes upward and inward. A guide protrusion is formed on an enclosing housing of the developing unit to slide along the guide rail to guide an installation of the developing unit into the case, and a handle is extended from the housing in a direction opposite to the guide rail with an upward slope.