Even when recording sheets (P) are fed from different storage means by switching over among a plurality of recording-sheet storage means (106a, 106b, 106c, 106d, 113), recording sheets are fed to image transfer means (101) always at a constant timing, so that the copying operation is executed at high copying efficiency and with reliability. Recording sheets (P) stored in a cassette (106a) are fed one by one to a conveyance path (108a) by a sheet feed roller (109a). The recording sheets (P) retained in an intermediate tray (113) are fed one by one to a conveyance path (115) by a sheet feed roller (114). The timings at which the sheet feed rollers (109a, 114), which are first drive rollers, are driven are controlled in such a way that a register roller (160), which is a second drive roller, can be driven at a constant cycle time with respect to a plurality of recording sheets (P) fed from the conveyance path (108a, 115). Even when the cassette (106a) and the tray (113) are switched over, the register roller (160) is driven always at a constant cycle time. Thus, the image forming operation can be executed by feeding recording sheets (P) in synchronization with the image-reading timing.