A press plate (8) with a cover (12) is moved upwardly from a standby position to a press position to press the cover against a book block (4) by first and second elevation units. The book block (4) is clamped by nip plates (9, 10), together with the cover (12). The height of each of first and second ends (X, Y) of the press plate (8) at the press position can be set separately by separately controlling the first and second elevation units by a control section (30).