PURPOSE: To suppress the occurrence of quenching by a method wherein the heat shrinkage rate of coil pressers in circumferential direction is made smaller than that of dipole coils and the coils in radial direction.

CONSTITUTION: Dipole coils 1 and coil pressers 2 in circumferential direction are retained in cylindrical shape by coil pressers 3 in radial direction having a relatively large heat shrinkage rate, and the angle of aperture θ of the coil pressers 2 in circumferential direction becomes larger than that which was before cooling due to the difference in their heat shrinkage by the relation between the dipole coil 1's heat shrinkage rate > circumferential direction direction coil presser 2's heat shrinkage rate and the radial direction coil presser 3's heat shrinkage rate > circumferential direction coil presser 2's heat shrinkage rate. The increase of the angle θ of aperture of the circumferential direction coil presser 2 when cooling results in compression of the dipole coil 1 in circumferential direction, and besides, the precharged pressure in radial direction when cooling is increase, and the dipole coil 1 becomes hard to move. As a result, the dipole coil is firmly fixed, and the occurrence of coil quenching can be suppressed.