An apparatus for detecting the amount of developer includes an agitation member for agitating developer contained in a developer container, and a detection member for detecting the position of the upper surface of the developer contained in the developer container, and interlocked with the agitating operation of the agitation member, the detection member is made movable above the upper surface of the developer. With the structure thus arranged, the remaining of the developer can be detected exactly even when the remaining developer become very small. Also, with the structure thus arranged, the operation of the detection member is finished in a position not to hinder the agitating operation of the agitation member, thus enabling the agitation member to continue its normal operation after the detection of the remaining developer is finished.