A method of manufacturing a washer capable of improving a material yield is provided. The method includes: a preparation step of preparing a longitudinal member which includes an upper corrugated portion and a lower corrugated portion including crest portions formed on at least one of an upper surface and a lower surface and valley portions continuous to the crest portions in the right-left direction; and a deformation step of deforming the longitudinal member such that the upper surface and the lower surface are arcuate as viewed in the direction from the front to the rear.