To provide a method and apparatus for forming the spine of a bookbinding block, capable of effectively performing bookbinding improved in registering.

Each of a plurality of pockets 20 has a wall 23 having first and second wall parts 26, 25 and the second wall part 25 is revolvable with respect to the first wall part 26. Each pocket 20 has a packer 29 and a spine restraining part 22 both of which are positioned at the lower end of the second wall part 25 coming into contact with the end of the spine 43 of a printed product 42 in a detachable manner. The printed product 42 is fed so as to impinge against the restraining part 22 in order to form the spine 43 and the spine restraining part 22 is separated from the spine 43 to be moved and the second wall part 25 is revolved with respect to the first wall part 26 to bend the printed product 42.