A valve timing control device includes a lock mechanism having a hole portion formed in one of the driving-side/driven-side rotational members, a sleeve in the hole portion, a lock member in the sleeve and capable of projecting and retracting with respect to the other of the driving-side/driven-side members, and a lock hole formed in the other of the driving-side/driven-side members such that the lock member can be fitted to the lock hole when the lock member projects. The lock mechanism constrains a relative rotational phase of the driven-side rotational member with respect to the driving-side rotational member at a predetermined phase when the lock member is fitted to the lock hole. A first chamfered surface is formed in the circumferential direction at an inner-circumferential corner of an end of the sleeve on the side opposite to the side facing the lock hole.