An image forming apparatus includes: toner supply amount detecting means for detecting a toner supply amount to a developer tank; detecting means for detecting a signal value of each pixel of an image; and toner consumption amount estimating means for estimating a toner consumption amount, based on the signal value. The signal value detected by the detecting means is corrected in accordance with the toner supply amount detected by the toner supply amount detecting means. The toner consumption amount is estimated based on the signal value corrected. This allows the toner consumption amount to be always calculated accurately, regardless of a variation amongst various models, or a variation in a toner consumption characteristic due to aging, using environment, or the like.