The present invention provides a development device which does not accumulate the developer at the corners on the internal walls, the process cartridge having such a development device, and the image forming apparatus, without increasing the size of the device or complicating its structure. A curving surface section is provided in at least one of four sections where internal walls in which bearings of the first rotary conveying body and the second rotary conveying body are positioned intersect with internal walls that are parallel to the first rotary conveying body and the second rotary conveying body.