A sealless accumulator 14, which intervenes between a solenoid valve 4 and a spool valve 5 for absorbing vibrations of a hydraulic oil concerned, is disposed in an upper half of a valve body above an oil path 18 formed in the upper half of the valve body 16. Air discharge path 24 is provided on an opposite side of an accumulator 14 from its oil chamber in which the oil pressure is applied to the piston 22 such that when the oil pressure is applied to the oil path 18, the piston 22 is moved, the hydraulic oil is discharged through the air discharge path 24 to the outside, possible air present up within the oil path 18 flows into the accumulator 14, and then is discharged through the air discharge path 24 to the outside.