A tape printer includes a holder support member at one side end in a roll sheet holder storage part in a direction substantially perpendicular to a feeding direction. In the holder support member, a mounting piece which is substantially rectangular in section and formed protruding outward on a positioning holding member of a roll sheet holder is fitted. The tape printer further includes a flat portion formed substantially horizontally between a rear edge of an insertion opening through which a roll sheet is inserted into the tape printer. On the flat portion, a front portion of a guide member is placed. At a rear edge of the flat portion in the feeding direction, at plural positions corresponding to various kinds of the roll sheets having different widths, there are formed four second positioning grooves in which part of the guide member is fitted.