PURPOSE: To provide an image forming apparatus which can carry out the optimum processing corresponding to the types of transfer paper sheets without requiring an increased number of sensors, and provide an image forming apparatus which can avoid image formation in vain as much as possible in the case where transfer for two sheets is carried out simultaneously, in image forming apparatuses in which input image is transferred once to an intermediate transfer body and the transferred image formed on the intermediate transfer body is transferred to a copy paper sheet.

CONSTITUTION: Regarding the image forming apparatus in which an input image is once transferred to an intermediate transfer body 9 and the transferred image formed on the intermediate transfer body 9 is transferred to a copy paper sheet 2, the apparatus is provided with a means to stop and make ready a copy paper sheet 2 when the copy paper sheet 2 passes an optical sensor 80 for tip end detection of the copy paper sheet 2 to be supplied to a transferring position and reaches a position at a prescribed distance from the sensor 80, a means to judge the type of the copy paper sheet 2 based on a signal of the optical sensor 80 obtained by the waiting time, a means to switch controlling contents of image formation corresponding to the result of the judgement of the prior means, and a means to retransfer the copy paper sheet 2 at the waiting position to the transferring position at the timing of transfer when a transferred image formed on the intermediate transfer body 9 is transferred to the copy paper sheet 2.