PURPOSE: To adjust valve clearances of intake and exhaust valves by only one lash adjuster.

CONSTITUTION: A lash adjuster for an internal combustion engine comprises a guide member 40 fixed to a cylinder head and having the openings on both ends, a first plunger 42 and a second plunger 44 reciprocatably mounted on the guide member; and first and second levers 70, 72 receiving the force from the first and second plungers for contacting a point of a rocker arm with the stems of the intake and exhaust valves. further the lash adjuster comprises a common chamber 52 receiving the hydraulic fluid applying a side pressure to the first and second plungers to maintain a contacting force of the rocker arm and the valve stem constant, the independent chambers 58, 60 inside of the first and second plungers capable of resupplying the hydraulic fluid into the common chamber when the valve is closed, and a check valve means for supplying the hydraulic fluid to the common chamber from the independent chamber side.