A reactor is disclosed. The reactor is comprised of a housing, a solenoid coil, a center columnar member, and a core. The center columnar member provides first surfaces contacting with sandwich portions of the housing, and the core is comprised of resin including magnetic powder. The coil and the center columnar member are fixed in the core. A surface roughness (Rz2) of a second surface which contacts to the core is larger than a surface roughness (Rz1) of the first surfaces. The center columnar member further provides a basis surface of which roughness (Rz3) is smaller than the Rz2 and larger than the Rz1.