An upstream-side printing unit group and a downstream-side printing unit group, respectively, are driven by separate prime motors and synchronously controlled. In addition to rotary encoders for the upstream-side and downstream-side prime motors, rotary encoders are provided on a last impression cylinder of the upstream-side printing unit group and a first transfer cylinder of the downstream-side printing unit group to detect differences between rotational phases, which the upstream-side and downstream-side printing unit groups should have, and the actual rotational phase of the last impression cylinder of the upstream-side printing unit group or the first transfer cylinder of the downstream-side printing unit group. In accordance with the rotational phase differences, the rotational speeds of the prime motors are corrected.