A reactor device includes a coil, a magnetic core having the coil thereon, a case accommodating the coil and the magnetic core, a cooling plate fixed to the case, an insulating sheet disposed between the coil and the cooling plate, a compressible graphite sheet disposed between the coil and the cooling plate, and a screw to fix the cooling plate to the case. The case has a screw hole and an opening provided therein. The screw passes through the screw hole to fix the cooling plate to the case. The coil contacts the insulating sheet through the opening of the case. The graphite sheet contacts the cooling plate. The reactor has high cooling performance and reliability.