Developing device having a residual toner amount discrimination feature

Abstract

A developing device is constructed by a developing unit for developing an electrostatic latent image on an image holding member, a developing agent containing unit for containing a developing agent which is supplied to the developing unit, an agitator, provided in the developing agent containing unit, for agitating the developing agent, a detecting sensor for detecting a residual amount of developing agent in the developing agent containing unit, and a determining device for determining the residual amount of developing agent at a plurality of levels on the basis of an output state of the detecting sensor in a predetermined time range. The determining device determines the residual amount of developing agent on the basis of a ratio of an output time of a developing agent presence state of the detecting sensor and an output time of a developing agent absence state in the predetermined time range. When a ratio at which the output time of the developing agent presence state of the detecting sensor occupies in the predetermined time range is equal to or less than a predetermined value, the determining device determines that the residual amount of developing agent is small, and when the ratio is substantially equal to 0, the determining device determines the absence of developing agent.