To obtain various kinds of reverberations by changing the ratio of a backward cosine length with respect to an effective string length.

A tailpiece structure has a tailpiece 21 for a cosine length 1/4 capable of changing the ratio of the backward cosine length L1 with respect to the effective string length L0 of a string 5 to 1/4, the tailpiece 22 for the cosine length 1/5 capable of changing the ratio to 1/5, the tailpiece 23 for the cosine length 1/6 capable of changing the ratio to 1/6 and the tailpiece 24 for the cosine length 1/8 capable of changing the ratio to 1/8 and the tailpiece 25 for the cosine length 1/10 capable of changing the ratio to 1/10. These tailpieces are selectively used.