A printer for printing a continuous sheet with position detection marks has a mark detection function and a feed amount detection function that are normally enabled. Further, the printer is provided with a mechanism that operates in a sheet feed mode (mark detection mode) that utilizes the mark detection function and a sheet feed mode (feed amount detection mode) that utilizes the set feed amount detection function. If the mark detection function suffers an error, the sheet feed mode is switched from the mark detection mode to the feed amount detection mode, and a printing operation is continued.