It is intended to provide an image forming apparatus that surely notifies a user of unit replacement timing and strongly urges the user to replace units without additional apparatus being applied thereto. A color printer 1 detects remaining life of each replaceable unit. When a certain replaceable unit nearly reaches its replacement timing, the color printer 1 indicates that fact in an operation panel 75. When the remaining life lowers improvement prohibiting level, in other words, when the unit reaches its replacement timing, the color printer 1 indicates a name of the unit to be replaced and necessity of replacement in the operation panel 75 and prohibits image improvement operation. That is, an image is formed without image quality improvement operation. Thereby, image quality deteriorates. Image deterioration can surely notify a user of replacement timing of the unit and urge the user to replace the unit with a new one.