PURPOSE: To compensate difference between the thickness of a plastic reel and that of a metal reel with thin thickness by a mechanism wherein covex portions are provided to a reel base while concave portions fitting to the convex portions are formed to the plastic reel in a reel base to which a reel of a magnetic tape is installed.

CONSTITUTION: A convex portions 3 are provided on a reel base 1 unified with a rubber disc 2 on the radial line of a plurality of pawls 5 formed on the central axis 4 of a reel base for driving a reel, which are disposed at regular intervals in the radial direction. Meanwhile, a plurality of concave portions 9 fitting to the said convex portions 3 are formed on the extension line of a plurality of thin grooves 8 provided at a central portion of a plastic reel 6 with thick thickness. The height of the convex portion 3 is set so that the height h of the plastic reel 6 to the reel base 1 become the same as height h in the case when a metal reel 10 with thin thickness is installed to the reel base 1 when the convex portion 3 is fitted to the concave portions 9 and the plastic reel 6 is mounted to the reel base 1.