PURPOSE: To enhance the extent of rigidity in the radial direction of a cam ring without making it into enlargement in the radial direction and a sharp rise in cost by connecting a reinforcing member, improving the rigidity in the radial direction of the cam ring, to an engaging part formed at both end faces.

CONSTITUTION: Each of reinforced plates 6, 7 is formed into the same diametral size as an outer diameter of a cam ring 1, while concave inner space parts 6a, 7a fitted with each other by a small diameter part 1b of this cam ring and a clearance of several microns are formed in one side, and each depth of these inner space parts 6a, 7a is set almost the same size with small diame tral part 1b of the cam ring 1. Thus, these reinforced plates 6, 7 are fitted with each other from both sides of the cam ring and used, whereby rigidity in the radial direction of the cam ring 1 is enhanced, and any deformation in the cam ring 1 due to high injection pressure is prevented from occurring. In addition, with these reinforced plates 6, 7 used, radial rigidity of the cam ring 1 is thus improvable without enlarging it in the radial direction.