PURPOSE: To prevent productivity from being lowered at a both-surface copying time or a composite copying time by maintaining the number of sheets of recording papers existing in a space making one round in a circulation type carrying path to be constant.

CONSTITUTION: Plural photosensors 241, 243 and 237 as a recording paper detection sensor are arranged at and after the inversion part 235 of the circulation type carrying path and used for measuring the position and the speed of the recording paper formed with an image on the first surface thereof, an interval between the recording paper and a paper supply means 2 and a time interval of the carry of the recording paper. The drive of a paper supply motor 225, a resist roller 229 and a carrying roller 232 is so controlled by a control part 26 as to maintain the number of sheets of recording papers existing in the space making one round in the circulation type carrying path to be constant while keeping a proper feeding interval when the recording paper is fed to an image forming means 4 by the paper supply means 3 or the recording paper is carried in the circulation type carrying path, based on the state information of the recording paper obtained based on the outputs of the recording paper detection means 241, 243 and 247.