Abstract: Provided is a mold core, a reactor having the mold core, and a manufacturing method of the mold core in which the leg portion connecting surfaces of the yoke portions are aligned at the same height and gaps are prevented from forming between the end surfaces of the leg portions and the leg portion connecting surfaces. The mold core 2 of the reactor 1 is made of a dust core and includes the yoke cores 41 for connecting a plurality of leg portions 32, and the yoke resins 42 for molding the yoke cores 41 by insert molding. The yoke cores 41 are divided into a plurality of core blocks 5 connected in a row without gaps, and the core blocks 5 include leg-portion-side blocks 61 that are connected to the leg portions 32 one-to-one.