To provide a crankshaft which can be strengthened in a short time and which is strengthened over a wide range while avoiding wasteful processing as a matter of course. This crankshaft comprises a fillet portion (15) between a crank pin (13) and a journal pin (11). A compressive residual stress is applied in approximately equidistant ranges in both circumferential directions from the portion of the fillet (15) where the greatest bending load acts, which is the center position, and the processing depth for applying the compressive residual stress gradually reduces in the circumferential direction away from the center position where the compressive residual stress is greatest.