A magnetic jammer for a card reader and structured to generate a magnetic field for jamming illegal reading of magnetic data stored on a card may include a core including magnetic material; a coil wound around the core and structured to generate a jamming magnetic field; a case accommodating the core and the coil; and a resin sealant filling the inside of the case and covering the core and the coil. The core and the coil may be disposed apart from an inner face of the case such that the core and the coil do not come into contact with the inner face of the case. A portion of the resin sealant may be disposed between the core and the inner face of the case and between the coil and the inner face of the case.