To effectively damp the vibration of not only strings but a racket frame as well by a method wherein at the center of a block of approx. the same width of the width of strings, a mushroom-shape vibrator is integrally connected, and on both side surfaces of the block, a vertical groove which is fitted between the strings, is provided.

At the center of a block 1 of approx. the same width as the width of strings (gut) made of rubber or plastic, a mushroom-shape vibrator 2 is integrally connected by punching out or molding, and on both side surfaces of the block 1, vertical grooves 3, 3 which are fitted between the strings 12, 12 are provided to constitute this vibration preventive device. At the time of use, the block is fitted in a space between the strings 12, 12 by fitting the strings 12, 12 in the vertical grooves 3, 3 of the block 1, and since the vibrator 2 is formed into a mushroom-shape, the vibrator can displace to the block 1 not only in the vertical and lateral directions wherein the strings 12, 12 are extended, but in the vertical direction as well based on the surfaces of the strings 12, 12. Also, by the inertia, the vibrator 2 stops not only the vibration of the strings 12, 12 but the vibration of the racket frame as well.