<p>A rocker arm (6) that is rockably attached to a cylinder head (1) actuates a valve (4) by means of a guide groove (73b) that is formed at an end thereof engaging with an upper end of a valve stem (41), and a roller (8) that is mounted in a roller housing portion (72) of the arm main unit (7) contacting against a cam (31) and rocking. The guide groove (73b) is formed by press working ends of the arm main unit (7) in the thickness direction of the plate material to form a pair of walls (73d), and thereafter applying sandwiching pressure in the lateral direction to the walls (73d) to increase the height thereof.</p>
