Image formation device

An image formation device

• including a photoreceptor configured to carry a toner image, a charging member configured to charge a surface of the photoreceptor, an exposure section configured to write an electrostatic latent image onto the charged surface of the photoreceptor, and a developer configured to form the toner image on the electrostatic latent image on the photoreceptor, and
• configured such that the photoreceptor is a replaceable photoreceptor unit, comprising:
• a photoreceptor use amount counting section configured to count a cumulative use amount of the photoreceptor unit;
• a charging bias application section configured to apply a charging bias to between the photoreceptor and the charging member and to measure, in other states than image formation, a charging current flowing between the photoreceptor and the charging member in a state in which the charging bias is applied to between the photoreceptor and the charging member;
• a film thickness decrease calculation section configured to calculate a decreasing gradient of a film thickness of the photoreceptor unit based on the measured charging current and the cumulative use amount of the photoreceptor unit in measurement;
• a film thickness decreasing gradient holding section configured to hold the film thickness decreasing gradient of the photoreceptor unit and to newly hold, when a film thickness decreasing gradient is newly calculated, a representative value of the previously-held film thickness decreasing gradient and the newly-calculated film thickness decreasing gradient;
• and
• a photoreceptor life management section configured to obtain a consumption rate of the photoreceptor based on the cumulative use amount of the photoreceptor unit and the film thickness decreasing gradient held by the film thickness decreasing gradient holding section at time of execution of the image formation.