PURPOSE: To increase the speed of a work to perform finishing cutting of the butt end and the top of a boot to be cut and perform punching of binding holes and to suppress breakage of the book to be cut and breakage of a punch for forming binding holes.

CONSTITUTION: A three-side trimming machine is formed such that the butt end and the top of a book to be cut are finish-cut by a vertical moving cutting blade and binding holes are formed by means of a built-in punching device. The punching device is attached to a frame 1a to which a cutting blade for a top is attached and provided with a punch 12 for forming binding holes vertically moved togetherwith the cutting blade, and a press metal 13 having an opening 17, through which the tip of the punch 12 for forming binding holes is inserted, and always energized downward against the force of a spring 20. Further, the punching device is provided with a shaft 14 for positioning which is designed to lift the press metal 13 against the force of the spring 20 and expose the tip part of the punch 12 for forming binding holes, and a die for forming binding holes installed corresponding to and below the punch 12 for forming binding holes.