An image forming apparatus, which uses a developing device including: a developer carrying member; a developer containing portion; an agitating member agitating a developer; a developer amount detecting member outputting a signal for detecting the remaining amount of the developer contained in the developer containing portion, the image forming apparatus including a main body controller detecting the remaining amount using a first detecting unit that sets a reference value as a reference for detecting the remaining amount by the signal, and thereafter calculates the remaining amount based on an amount of change in the signal from the reference value, and a second detecting unit that detects the remaining amount based on a band of fluctuation in the signal corresponding to a rotational period of the agitating member.