Parts having a strength distribution were produced from tailor friction-welded billets consisting steel bars having different quenchabilities. JIS-SCr420 having high quenchability and JIS-S25C having low quenchability were joined by frictional welding. The tailor friction-welded billet was then forged, and the forged billet was quenched to induce a strength distribution. The formability of the tailored billet was examined from compression tests in compression in directions normal and parallel to the interface. For the 80% compressed tailored billets, no cracks were observed. In a tensile test of a specimen cut from the 80% compressed tailored billet in the parallel direction, the fracture occurred on the JIS-S25C side having a low flow stress, not at the interface. By annealing the tailored billet, inhomogeneous deformation around the interface was prevented. A shaft having a high strength flange and a connecting rod having high strength and machinability were produced by forging and quenching the tailored billet.