To make a permanent-magnet synchronous motor operable under a higher-temperature condition, by simultaneously adding Si and C to the material of the magnet of the motor at mixing ratios of specific atomic percentages.

In order to reduce the absolute temperature coefficient value of the coercive force of the Nd-Fe-B magnet material of a permanent-magnet synchronous motor composed mainly of an Nd2Fe17B compound, Si and C are simultaneously added to the magnet material. The magnet material is manufactured by the powder-metallurgial processing, melt quenching method, etc. The Si and C in the magnet material are entirely or partially occluded in the Nd2 Fe17B main phase of the material, change the distortion of the crystal lattice or magnetically coupling state between elements, and affect the temperature- dependence of the magnetic anisotropy of crystals in the main phase. It is preferable to adjust the adding amount of Si and C to 0.05-2.0 at.%. Therefore, the coercive force decreasing rate of the magnet material with temperature becomes smaller and the limit usable temperature of the material can be improved extremely.