A cam lobe piece of a built-up type camshaft for an internal combustion engine. The built-up type camshaft includes a hollow shaft fixedly inserted in a shaft opening of the cam lobe piece upon diametrical expansion of the hollow shaft. The cam lobe piece comprises a base circle section having the shaft opening, and a cam lobe section formed integral with the base circle section. In this cam lobe piece, the cam lobe piece is formed of a ferrous sintered material which has a density (ρ) meeting the following equation ρ (g/cm 3 ) ≥ - 3/8 × t + 8.9 where t is a thickness (mm) of the base circle section in radial direction.