An image forming apparatus includes a photoconductor, a charging roller for charging the photoconductor, a current sensor for detecting a value of current flowing through the photoconductor or the charging roller as a result of application of voltage to the charging roller, an acquisition sensor for acquiring an environment value representing an environment state inside the image forming apparatus, and a processor configured to estimate a film thickness of the photoconductor, based on a value of current detected by the current sensor when a state in which the environment value falls within a predetermined range continues for a predetermined time or longer.