To suppress abnormal sound generated by oil shortage of a high pressure chamber even in a case where a lash adjuster is downsized.

A storage wall 13 is formed in the upper end part of a body 10 of a lash adjuster 1, and a storage section 15 for storing oil is formed by the inner peripheral surface of the storage wall 13 and the outer peripheral surface of a plunger 20 opposite to the inner peripheral surface. An introduction hole 22 is formed on a peripheral surface 21 of the plunger 20. An introduction groove 29 for introducing the oil in the storage section 15 to the introduction hole 22 by a self-weight is formed on the outer peripheral surface of the plunger 20.