PURPOSE: To improve precision and work efficiency in a case in which a finger hole and a balance hole are piercingly provided at a bowling ball.

CONSTITUTION: A frame body 20 to swing back and forth by the operation of a handle 26 is provided on a slide table 1 that is guided by means of rails 6 or the like and is delivered back and forth and right and left on a base stand 3 by the operation of handles 4, 5, and a ball mounting stand 29 to swing right and left by the operation of a handle 35 is provided on its inside. Clamp arms to be operated by means of an air cylinder are provided on both front and rear sides of the ball mounting stand 29, and a cross line projector 39 by means of laser rays is provided at the front of a main spindle head 41, and the positioning of a ball B supported on the ball mounting stand 29 is conducted by using this projector 39. Next, the ball B is pinched by means of a pair of front and rear clamp plates provided at the upper end portion of the clamp arms and fixed, and then, the position of a hole of the ball B to be bored is made to coincide with the spindle core of a drill D by the operation of the handles 4, 5, 35, and then, boring is started.