Abstract: Printing apparatus for printing one or both sides of single sheets fed consecutively to the printing apparatus, with a printing channel with an associated printing station and paper-transport elements. The printing channel is coupled on the entry and exit sides to a return channel which has paper-transport elements and a turning device and which, as required, after the printing of a front side feeds the single sheets to the printing station once again for the printing of the reverse side. The printing channel is followed by a paper-transport channel system having paper-transport elements and with a separate duplex channel and simplex channel for the separate transport of the single sheets printed on both sides or on one side into a common output channel with a second turning station for the duplex sheets.