An image forming apparatus provided with a control circuit disposed at a front position of transfer section for correcting the timing of signal emission for turning on register rollers and also for starting exposure for image formation. The control circuit corrects the timing of signal emission basing on the time measured from signal emission to the time when the leading edge of a paper sheet reaches a sensor disposed at a rear position of the register rollers. The correction is made every time when a predetermined number of sheets are fed or an average value based on a predetermined number of samplings is obtained or power supply is turned on. The correction is further made by memorizing the data practically measured on the number of sheets fed to the transfer section from each one of paper feed positions.