A reactor comprises a coil member and a core member. The coil member comprises an insulation-coated conductive wire and an insulation coating. The insulation-coated conductive wire is wound and coated, at least in part, with the insulation coating. The core member comprises a first member and a second member. The first member has a relative permeability higher than another relative permeability of the second member. The second member includes a composite magnet, and the relative permeability of the second member is between 1 and 30 (both inclusive). The composite magnet is formed of a hardened binder and magnetic particles dispersed in the binder. The composite magnet has an elastic modulus that is one hundred times or more than another elastic modulus of the insulation coating.