A method for manufacturing a forged crankshaft includes a die forging step for obtaining forged material formed into the shape of a crankshaft by die forging and a reduction step for reducing forged material (30) by a pair of first molds (10). The forged material (30) has first excess parts (Aca, Ada) protruding from the outer periphery of side parts (Ac, Ad) in the vicinity of journal parts (J) on all or part of arm parts (A) having integrated weight parts (W). In the reduction step, the first excess parts (Aca, Ada) are reduced and deformed by the first molds (10), and the first excess parts (Aca, Ada) are pulled out to the pin part (P) side. Thus, a forged crankshaft that simultaneously achieves weight reduction and high rigidity can be obtained simply.