To provide a method for manufacturing a crankshaft by which force for bend correction can be secured while the occurrence of flaw caused by burr is prevented, and the wear of a corner part of a sizing die can be avoided, and to provide a forming die used therefor.

Parting lines (P/L) in both parts 11A, 11B of a crankshaft blank 11 formed with press die, are inclined from a horizontal direction to a twisting direction of a twist forging performed in a post-process [Figure 1 (A)] and the parting lines at these both end parts are positioned in the same plane after twist forging. When the sizing-formation is then performed by using the sizing die [Figure 1 (D)], the parting lines at both end parts in the crankshaft blank 11 subjected to twist forging are set be perpendicular to the sizing-forming direction S.