Reactor and manufacturing method of reactor

A manufacturing method of a reactor including a coil, two I-shaped I-cores, and an O-shaped O-core configured to surround the two I-cores, the manufacturing method at least comprising:

• a coil mold step of forming a coil mold in which a first resin is molded to cover at least part of the coil;
• and
• a main body mold step of forming a main body mold in which a second resin is molded to cover at least part of an assembly body in which the coil, the coil mold, the two I-cores, and the O-core surrounding the coil and the coil mold are assembled, the two I-cores being placed inside the coil such that the two I-cores are arranged side by side, wherein:
• in the coil mold step, a first gap plate configured to fill a gap between positions where the two I-cores are placed is formed by molding with the first resin;
• and
• in the main body mold step, second gap plates each configured to fill a gap between the O-core and a corresponding one of the I-cores are formed by molding with the second resin.