An image forming apparatus includes: an image carrier that rotates and carries a toner image by a surface layer disposed on a surface thereof; a charging roll that charges the surface layer while the image carrier completes one or more rotations; a power supply unit that supplies a current to the charging roll; a detector that samples and detects the current that the power supply unit outputs; a leak current detector that detects a leak current included in the current that the detector has detected; a layer thickness calculating unit that calculates a numerical value relating to the thickness of the surface layer on the basis of the current that the detector has detected; and a current leak state determining unit that determines a current leak state on the basis of the current that the detector has detected and the leak current that the leak current detector has detected.