A reel spring for tape cassettes includes at least two mounting holes which are formed in the base portion at opposite sides with respect to a tape reel centerline connecting reel centers and in such a manner to be spaced in the direction of the tape reel centerline, and which is used for melt-bonding with the cassette housing. The base portion is arranged so as to have a center laid on the tape reel centerlines, respective end portions are arranged so as to have their centerlines passed through respective contact points for urging a pair of tape reels, extended in parallel with each other and deviated with respect to the tape reel centerlines. The width of the base portion is substantially the same as that of the end portions. The reel spring is prepared through a cutting step for cutting a stock up to positioning holes from opposite edges of the stock so that the cutting is made with the same width as the width of a reel spring end portion, along separation lines which deviate with respect to the tape reel centerline, extend in parallel with one another and pass in the vicinity of the mounting holes, the separation lines including separation lines for reel spring end portions at one side and separation lines for reel spring end portions at the other side which are out of alignment.