A method of manufacturing a reactor includes a pair of coils and a pair of core units of partial I-shaped cores with gap members butted together and mounted in the coils. The respective ends of the I-shaped cores are pressed against the ends of a pair of U-shaped cores. The U-shaped cores and the I-shaped cores are formed by pressing powder in movable dies that preheat any burrs formed during pressing to be positioned in a direction different from the winding axis direction to avoid any contact with the coil.