PURPOSE: To easily set the pressing force of a pressing board accurately to a desired value by using a pressure detector setting hydraulic pressure in an oil passage, that is, pressing force of a pressing piston in the pressing board.

CONSTITUTION: Engaging a rotary tool with a hexagonal hole 41 in a threaded shaft 40 to be rotated and advancing the threaded shaft 40 to be screwed to the side of a pressurizing chamber 37, when a pressurizing piston 39 is moved being pressed to the pressurizing chamber 37, a device, pressing a pressure detecting piston 35 to the side of its small contour part 36 and adapting a stepped part of the piston 35 to the stepped part of a piston hole 34 while increasing a pressure of oil in an oil passage 43, displays the pressure in a pressure gage 44. And when pressing force of a pressing piston 4 in a pressing board is adjusted to a desired value, the device, fitting a threaded shaft part 33 of a pressure detector to be screwed to a threaded hole 19 in the pressing board and inserting the small contour part 36 of the pressure detecting piston 35 penetrating through a stopper plug 22 of the pressing board to be adapted to a pressure detecting piston 21, mounts the pressure detector 31 to the pressing board 1. Next the device, when it sets the pressing force of the pressing piston 4 to about 9t, is required to only set the pressure of oil in an oil passage 10 in the pressing board to about 260kg/cm2.