A method of manufacturing a reactor is provided. The reactor include: a coil including a wound flat wire, the flat wire being covered with an insulating film, and the coil having a flat surface; and a cooler facing the flat surface, in which the flat wire on an outer periphery side of the coil may be not covered with the insulating film at the flat surface, and the flat wire at the flat surface may include a plurality of wire segments lying in a pitch direction. The method may include pressing a rod against a short side of the plurality of wire segments to form at least one thickened portion in each of the plurality of wire segments, the thickened portion being a portion of the flat wire thickened in the pitch direction.