When the upper case of the developing device is pushed from above, the upper case may be deformed producing a negatively activated pressure corresponding to the deformed volume of the case, thereby dispersing toner along with the air. When the developing device is mounted to or dismounted from the color image forming apparatus, the dispersed toner may fall out of the developing device. To prevent the toner from falling out of the developing device, the toner carrier and the limiting member for limiting the toner layer thickness are held in the developer case and a falling toner receiver is formed which is recessed in the developer case in the longitudinal and widthwise directions of the toner carrier and the limiting member for limiting the toner layer thickness. The falling toner is collected in the receiver, preventing the device from being contaminated with the falling toner and facilitating the cleaning of the device.