Abstract: An apparatus for adjusting an operating speed of a pneumatic valve 1 by means of a solenoid valve 2 including a disk-shaped orifice block 5 having a plurality of orifices 22-25 of different aperture sizes formed therein, and the orifice block is arranged rotatably between a sub-base 3 of the solenoid valve 2 and a main block 6. By rotating the orifice block 5, any one of said plurality of orifices formed in the orifice block 5 can be selectively inserted into the fluid passage between the pneumatic valve 1 and the solenoid valve 2. The operating speed of the pneumatic valve 1 can be easily adjusted in a digital manner, and the water hammer phenomenon can be effectively prevented.