A printer is operable for image formation onto a sheet of a sheet width Lp, with a sheet spacing Lg and a printing transfer speed Vg, a constant speed transferrer makes sheet transfer at the printing transfer speed Vg from a register via the printer to a speed change position, a variable speed transferrer makes sheet transfer from the speed change position to the register, and a transfer controller controls sheet transfer speeds, the variable speed transferrer having sections for sheet transfer, including deceleration and acceleration sections for sheet reversal at the sheet reversing path, and a constant speed section for transfer at a constant transfer speed Vr, the transfer controller determining a circulating sheet number N, executing a calculation of transfer speed Vr employing sheet width Lp, sheet spacing Lg, printing transfer speed Vg, and accelerations, to enable sheet transfer for circulation within a time interval of N×(Lp+Lg)/Vg.