To reduce an eccentric load caused on plural numbers of buffer hydraulic cylinders and to automatically and efficiently search the most suitable buffer position with a few shot by repeating of correcting the position of each buffer piston so that the difference, etc., of the max. value of hydraulic pressure of each buffer hydraulic cylinder is made smaller.

In an initial time to start searching, until the max. value of hydraulic pressure of all the buffer hydraulic cylinder 10 is made more than, a prescribed value, because only the buffer piston being not yet filled to the prescribed value is raised roughly by every 1st prescribed distance, so this piston is made rapidly in contact with a guide post 4. Further, after then, the piston is raised by every 2nd prescribed distance made smaller than the 1st prescribed distance. In this time, because correcting the position of each buffer piston 12 is repeated alternately so that the difference, etc., between the max. values of hydraulic pressure of each buffer hydraulic cylinder 10 is made within the prescribed value, the height difference of position of all the buffer piston is made small. Therefore, the generation of the eccentric load in the press machine can be reduced.