A cam housing 3 in accordance with the present invention includes: a body portion 4 that is provided separately from a cylinder head 1, supports a camshaft 2 for driving a valve 10 provided in the cylinder head 1, and is fixed to the cylinder head 1; a sub housing 20 that includes a mounting concavity 21 for mounting a lash adjuster 18 and is fixed to the body portion 4 with a mounting face 20A thereof forced against an outer face of the body portion 4, the mounting face 20A being different from the face wherein an opening of the mounting concavity 21 is provided; and
an air vent 22 that penetrates the sub housing 20 between a wall surface thereof and the mounting face 20A thereof and thereby is provided in the sub housing 20, the wall configuring an inner space formed in the mounting concavity wherein the lash adjuster 18 is mounted.