A reactor includes a coil and a core unit having partial cores butted against one another to form a closed magnetic path. The partial cores include a first partial core forming and a second partial core. The first partial core is inserted in the hollow of the coil. A pressed face of the first partial core is oriented orthogonal to the winding axis direction of the coil. The second partial core is butted against the first partial core. A pressed face of the second partial core is oriented orthogonal to a direction different from the winding axis direction. The pressed face of the second partial core is a substantially flat plane.