Abstract: An image forming device includes a device body, a cartridge detachably attached to the device body so as to accommodate material which includes one of consumable material and waste material, a sensor configured to emit and receive sensing light and give a detection value corresponding to an amount of the material in the cartridge which amount is detected based upon an intensity of the sensing light received thereby, a received light changing member configured to change the intensity of the sensing light received by the sensor, and a judging unit configured to judge based upon a change of the detection value given by the sensor whether the cartridge is a new one.

Abstract: 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.