PURPOSE: To facilitate mouning of a locker arm having a hydraulic lash adjuster (hereinafter referred to as HLA) on a cylinder head in a valve system of an engine.

CONSTITUTION: A guide part 19 is formed on a boss part 18 of a locker arm 12. A locker shaft 6 is inserted into the boss part 18, and a spring 8 is coiled around the locker shaft 6. The spring is compressed and the tip of the gide part 19 is brought into contact with the end surface of a bearing part 2 of a cam shaft 3 provided in the center part of the cylinder head 1, and the tip of a bolt 7 is screwed into the bearing part 2. When the bolt 7 is tightened, the guide part 19 is guided along the end surface of the bearing part 2, and the locker arm 12 is moved. The HLA mounted on the valve side of the locker arm 12 lifts the valve, and the locker arm 12 is mounted on the specified position. Since the locker arm 12 is guided to the end surface of the bearing part 2 by the guide part 19, it is unnecessary to compress the spring when the bolt is tightened, and mounting of the locker arm 12 on the cylinder head 1 is facilitated.