An image forming apparatus that prevents fraudulent alteration of the working life of a replaceable unit is provided. The unit includes a first memory that can store the consumed amount of the unit, and a second memory that has a plurality of flags. "OFF" of each of the flags is not changeable to "ON". The image forming apparatus includes a portion that counts upward a stored value of the first memory associated with use of the unit and the portion initializes the first memory when the stored value of the first memory exceeds the maximal value. The portion changes the state of any one flag in "ON" of the second memory to "OFF". The image forming apparatus also includes a portion that judges the working life of the unit based on the stored value of the second memory and the portion signals the working life.