To provide a developing device by which the occurrence of abnormal noise caused by a toner control member in press contact with a photoreceptor is restrained.

This non-magnetic one-component developing system device is provided with a toner hopper 11 having a toner flow-out port where toner is accumulated and the accumulated toner flows out, a developing roller 14 holding the toner flowing out from the port 13 and carrying it to the photoreceptor, a supplying roller 15 supplying the toner to the developing roller, and a developing blade 16 controlling the toner carried by the developing roller and forming a toner thin layer on the surface of the developing roller. In the device, a sensor (toner remaining amount detecting means) 21 detecting the remaining amount of the toner accumulated on the toner hopper is arranged, so that a detecting part is higher than the upper end edge of the toner flow-out port on the toner hopper, and the toner remaining amount detecting means is attached to a wall forming the upper side edge of the toner flow-out port.