An image forming apparatus of the present disclosure includes a developing device and a toner storage container. The toner storage container is detachable and attachable with respect to an apparatus main body. The toner storage container includes a supply screw which conveys toner by rotating forward, and a first engagement unit coupled via a gear train to a rotation shaft of the supply screw. The apparatus main body includes a second engagement unit which engages with the first engagement unit to restrain detachment/attachment of the toner storage container by engaging with the first engagement unit. In a case where an amount of toner in the toner storage unit has become equal to or less than a predetermined amount, a control unit makes the supply screw rotate backward to thereby release engagement between the first and second engagement units.