A check valve part includes: a valve seat hole into which hydraulic oil flows; a valve seat formed around the valve seat hole; a lateral hole formed to have an axis intersecting an axis of the valve seat hole; and a valve body provided so as to be separated from the valve seat or abutted against the valve seat. The valve timing adjustment device further includes a back pressure oil passage that communicates a space opposite to the valve seat with respect to the valve body with the lateral hole.