To provide a method for manufacturing exterior parts for a built-up camshaft which improves productivity and hardness of cam lobes.

A cam-piece continuous body 6 is chilled (transformed to white iron) by undergoing rapid cooling by a chiller 4 right after pouring the molten metal. As a result, the cam-piece continuous body 6 has a very high hardness on one hand, but decreased tensile strength and shearing strength on the other. In the cast cam-piece continuous body 6, cam-piece original shapes and notches are formed in an alternating sequence. The cam-piece continuous body 6 is held in a holder, and in that state, one stoke is given to the notch by a breaking tool, then the cam-piece continuous body 6 of the decreased tensile strength is broken at the notch of the easily breakable part. Thus, individual cam pieces are obtained.