To prevent oil from leaking through a sliding hole or the like as securing good longitudinal slidability of a lock pin as well as to prevent deterioration of valve timing control accuracy and improve durability of a timing belt.

Opening and closing timing of an intake valve is made variable by converting the relative rotation phase of a timing pulley 1 and a cam shaft 2 by making a vane 3 relatively rotatable with the timing pulley 1 reciprocatingly rotatable by means of feeding and discharging relative oil pressure to and from an advance side oil pressure chamber and a lag angle side oil pressure chamber. A through hole 50 is axially formed in the interior of a lock pin 34 of a lock mechanism restricting relative rotation of the vane 3 and the timing pulley 1 and oil is prevented from leaking to the external by making the interier of a slide hole 35, a space 51 and the like air tight as well as to obtain good slidability of the lock pin 34 by making air and oil inside a first and a second space 51 and the like substitutively flowing through the through hole 50 when the lock pin 34 slides longitudinally.