Patent ID: 7907854

Claim:
An image forming apparatus, comprising: a photoconductor driven to rotate and having a photosensitive thin film formed on its surface; a charging member that charges the photosensitive thin film of the photoconductor; a voltage applying unit that applies voltage of a DC component and voltage of an AC component to the charging member; a control unit that determines a film thickness measuring mode is enabled: a capacitance unit connected to a superposition point for the DC component and the AC component; a DC current measuring unit that measures the value of DC current passed from the charging member to the photoconductor when the voltage applying unit applies both voltage of a DC component and voltage of an AC component to the charging member during the film thickness measuring mode; a retract driving unit that separates the charging member from the photoconductor; and a capacitance measuring unit that measures the electrostatic charge amount of current coming into the capacitance unit when the voltage applying unit applies the voltage of a DC component to the charging member during the film thickness measuring mode, wherein the control unit integrates the DC current value measured by the DC current measuring unit with time for which the voltage is applied to the photoconductor and calculates a charge amount to determine a thickness of the photosensitive thin film from the electrostatic charge amount measured by the capacitance measuring unit and a result of the integration.