Breather device of internal combustion engine

A breather device of an internal combustion engine having a plurality of cylinders arranged in a row, comprising;

• a head cover main body having an upper wall extending over at least a large part of a cylinder head of the engine and including a downwardly recessed part, and a peripheral wall depending from a peripheral part of the upper wall, a lower end of the peripheral wall abutting the cylinder head to define a valve actuation chamber jointly with the cylinder head;
• a chamber forming member attached to the upper wall of the head cover main body so as to define a breather chamber extending in a cylinder row direction in cooperation with the upper wall of the head cover main body;
• an upstream breather passage communicating a first end of the breather chamber with a crank chamber;
• a downstream breather passage communicating a second end of the breather chamber with an intake passage;
• an oil return passage formed in the cylinder head to communicate the valve actuation chamber with the crank chamber;
• a first communication hole formed in a lower part of the downwardly recessed part adjoining the first end of the breather chamber to communicate the breather chamber with the valve actuation chamber;
• and
• a second communication hole formed in a part of the breather chamber downstream of the first communication hole to communicate the breather chamber with the valve actuation chamber.