PURPOSE: To prevent the degradation of the picture quality by specifying the arrangement of an erase means, a transfer means, and a sheet detecting means and erasing an unnecessary electrification potential at the time of detecting the trailing end of a transfer sheet or after the elapse of a prescribed time.

CONSTITUTION: Respective means are arranged to satisfy relations A≤B where A is the distance from the transfer position of a transfer means 20 on a photosensitive body 18 to the erase position of an erase means 30 and B is the distance for which the transfer sheet is carried from the transfer position to the sheet detection position of a sheet detecting means 6. When the trailing end of the transfer sheet is detected by the sheet detecting means 6 or the prescribed time elapses, the erase means 30 is operated. Thus, the unnecessary electrification potential is erased without increasing the cost even if the size of the used transfer sheet cannot be detected, and the degradation of the picture quality is suppressed.