PURPOSE: To reduce the cost of a mechanism by engaging the engaging projecting part of an offset adjusting member with arbitrary one of plural recessed parts formed on a fixed member and changing the position of the engaging projecting part to plural recessed parts.

CONSTITUTION: An offset adjusting member 129 which is supported freely turnably with a fulcrum as the center and for which an engaging projecting part 135 is formed at the position apart from the axial line of turning is provided and a fixed member 130 which is fixed in the vicinity of the offset adjusting member 120 and has plural continuous recessed parts formed in the peripheral edge part along the turning locus of the engaging projecting part is provided. One end of a band 143 is fixed at the position eccentric from the fulcrum of the offset adjusting member 120, and the engaging projecting part 135 is engaged with arbitrary one of plural recessed parts. When the offset adjusting member 120 is turned to engaged the engaging projecting part 135 with another recessed part, the strength of pressing of the band 143 to a drum part 64 of a reel base 60 is changed to adjust the offset of the tape tension.