PURPOSE: To improve production capacity in die casting machine, etc., by driving a die clamping cylinder at low pressure till giving increase pressure working signal, working an increase pressure piston at the time of giving the increase pressure working signal and increasing supplying pressure into the die clamping cylinder.

CONSTITUTION: In a die clamping cylinder device, the die clamping cylinder 1 and an increase pressure cylinder 2 are set. In the increase pressure cylinder 2, the cylinder 7 having a first and second chambers with different inner diameters and the increase pressure piston 8 having small and large diameter parts 8A, 8B conformed to the inside shape of the cylinder 7, are arranged. After giving a die closing command signal, the die clamping cylinder 1 is driven with the low pressure till giving the increase pressure working signal. At the time of giving the increase pressure working signal, by working the increase pressure piston 8, the supplying pressure into the die clamping cylinder 1 is increased. By this method, the time required for die clamping and the die opening in the die casting machine, etc., can be shortened.