To prevent a guard device for a gutter from giving a foreign matter feeling and an overpower feeling to a player by providing a frame, bumpers and plural rocking arms and parallelly moving the bumpers between the position of preventing the falling of a ball into the gutter and a bumper storage position by the rocking arms.

The bumpers 13 and 14 provided with a length over almost the entire length of a bowling lane 1 are disposed on both left and right sides of the frame 3W. The rocking arms 15 and 16 of the same length for supporting the bumpers 13 and 14 are provided, the inner ends of the rocking arms 15 and 16 are freely horizontally rockably and pivotally attached to the outer side walls of both left and right side frames of the frame 3W and the outer end parts are freely horizontally rockably and pivotally attached to the inner sides of the bumpers 13 and 14. By the rocking arms 15 and 16, the bumpers 13 and 14 are horizontally moved between a projecting act position for preventing the ball B from falling into the gutter 2 and the bumper storage position.