An image forming apparatus of forming an image corresponding to image data is formed on a recording medium comprises a data processor which performs data processing of input image data so that a first correlation will be established between a target image density expressed by the input image data and the actual image density of an image formed on the recording medium, thereby generating output image data, an image forming unit which forms an image corresponding to the output image data on the recording medium, and a toner consumption amount calculator which calculates a toner consumption amount which is consumed for image formation based on the input image data and based on a second correlation between the input image data and an adhering toner amount on the recording medium.