To provide a dummy shaft for a rocker arm facilitating assembly work of the rocker arm, reducing cost of whole assembly system, and facilitating washing to enable reuse.

The dummy shaft 10 is formed of synthetic resin material and shaft length thereof is roughly same as length of each shaft bearing hole 21 in an axial line direction at a time that the rocker arm 20 is assembled. The dummy shaft 10 is a straight cylinder body opening on both end as indicated in Fig. a. An end surface 12 of a cylindrical part 11 and a shape of a section at an arbitrary position in an axial direction (section indicated by line X-X in Fig. a) are same (refer Fig. b). The end surface 12 and the section is a rectangular in which an arc edge 13 and a straight edge 14 mutually adjoin. Thickness of each arc edges 13, 13 and each straight edges 14, 14 are roughly same.