In an image forming apparatus, a driving mechanism rotates a bottle attached to a bottle attaching portion by engaging with a first end of the bottle. A cover member, positioned to face a second end of the bottle, is supported to be able to open and close an opening from which the bottle is inserted. An elastic member applies upwards elastic force to the bottle attaching portion. A level sensor detects a position of the bottle attaching portion in an up-down direction. A signal processing device executes a full-state notifying process when a detection signal of the level sensor during operation of the driving mechanism fails to satisfy an abnormality condition, and the position indicated by the detection signal is lower than a predetermined reference position. The abnormality condition includes either or both of an amplitude condition and a cycle condition for a rotation cycle of the bottle.