In a sheet bundle printing system, a sheet is fed by peeling an uppermost sheet from a sheet bundle. A printing device has a printing head and a platen roller for printing on the sheet. An ink ribbon is fed through space between the printing head and the platen roller in parallel with the sheet at the time of printing thereon. The platen roller is moved back and forth relative to the printing head between a printing position in which the platen roller is urged into contact with the printing head and a contact-free position in which the platen roller is out of contact with the printing head. Ink-ribbon feeding is suspended in a manner interlocked with the relative movement of the printing head and the platen roller between the printing position and the contact-free position.