PURPOSE:To accurately measure the characteristic of a photosensitive body corresponding to a time point for executing tens of thousands of image formations in a short time, when the characteristic of the photosensitive body used for an image forming device is measured. CONSTITUTION:As a conditions setting element 3, an electrifier 32 connected to a high voltage power source 31, an exposure device 33, and an eraser lamp 35 connected to a destaticizing power source 34, are arranged in the vicinity of the photosensitive body A, and simultaneously, as a measuring element 4, a potential sensor 42 connected to a surface electrometer 41, is disposed. Further, as a temp. adjusting means 5 adjusting the temp. of the photosensitive body A, a panel heater 51, and a controller 52 controlling the temp. of the panel heater 51 are provided inside the photosensitive body A, and the temp. of the photosensitive body A can be adjusted by the panel heater 51 and the controller 52.