A simple precooling system for a superconducting magnet is developed using a Cryomech GB02 cryocooler and gas filled thermal switches. A superconducting magnet (NbTi wire, 7 T of maximum field, 5.6 kg of weight) is precooled to 16 K in about 70 h without any manual control. Heat transfer rate of each thermal switch (H2or N2gas filled at 1.3 MPa at room temperature) is about 3×10−1W/K during the ON state, and 5×10−3W/K during the OFF state.