PURPOSE: To surely support both ends of rocker shafts while securing a lubricating function by arranging the end sections of a pair of split rocker shafts face to face between a rocker bracket and a cap, and forming a cap side lubricant passage connected to a rocker shaft side lubricant passage on the cap.

CONSTITUTION: End sections 23a of a pair of split rocker shafts 23 are arranged face to face on a fitting seat 21a formed on the rocker bracket 21 of an engine, and the end sections 23a of the rocker shafts 23 are pressed to the rocker bracket 21 side by a cap 25. An eye bolt 27 is inserted into the cap 25 and the notch grooves of the rocker shafts 23, and the tip section is screwed to the rocker bracket 21. A lubricant passage 21d formed on the rocker bracket 21 is connected to a branch passage 23d formed on the coupling section of a rocker arm 31 through the lubricant hole 27a of the eye bolt 27, a cap side lubricant passage 25a, and a rocker shaft side lubricant passage 23c, thus the lubricating function of the sliding portion of the rocker arm 31 is secured.