A permanent magnet synchronous motor comprising: a stator; and a rotor, the stator including: a stator core that is formed by layers of magnetic steel plates, the stator core including magnetic pole teeth, each magnetic pole tooth being formed between adjacent slots; and stator windings that are provided in the slots of the stator core, the rotor, which is placed on an inner circumferential side of the magnetic pole teeth of the stator via an air gap, including: a rotor core that is formed by layers of magnetic steel plates; a plurality of magnet retaining holes formed in the rotor core along an outer circumference of the rotor core; permanent magnets inserted in the magnet retaining holes; and a plurality of slits (6, 61-67) formed in the rotor core on an outer circumferential side of the magnet retaining holes, the slits being elongated from a vicinity of the permanent magnets to a vicinity of the outer circumference of the rotor core, wherein among the plurality of slits, slits formed in a vicinity of a magnetic pole center of the rotor core are oriented in one direction and slits (61, 67) formed in a vicinity of a pole border portion of the rotor core are oriented in another direction that is different from the direction of the slits formed in the vicinity of the magnetic pole center of the rotor core, characterized in that a width in a radial direction of an outside narrow bridge in the pole border portion is larger than a width in the radial direction of another outside narrow bridge, the outside narrow bridge in the pole border portion being a part of the rotor core on the outer circumferential side of a magnet retaining hole in a vicinity of the pole border portion of rotor, and the another outside narrow bridge being a part of the rotor core on the outer circumferential side of one of the slits (61, 67) formed in the vicinity of the pole border portion. a stator; and a rotor, the stator including: a stator core that is formed by layers of magnetic steel plates, the stator core including magnetic pole teeth, each magnetic pole tooth being formed between adjacent slots; and stator windings that are provided in the slots of the stator core, the rotor, which is placed on an inner circumferential side of the magnetic pole teeth of the stator via an air gap, including: a rotor core that is formed by layers of magnetic steel plates; a plurality of magnet retaining holes formed in the rotor core along an outer circumference of the rotor core; permanent magnets inserted in the magnet retaining holes; and a stator core that is formed by layers of magnetic steel plates, the stator core including magnetic pole teeth, each magnetic pole tooth being formed between adjacent slots; and stator windings that are provided in the slots of the stator core, the rotor, which is placed on an inner circumferential side of the magnetic pole teeth of the stator via an air gap, including: a rotor core that is formed by layers of magnetic steel plates; a plurality of magnet retaining holes formed in the rotor core along an outer circumference of the rotor core; permanent magnets inserted in the magnet retaining holes; and a rotor core that is formed by layers of magnetic steel plates; a plurality of magnet retaining holes formed in the rotor core along an outer circumference of the rotor core; permanent magnets inserted in the magnet retaining holes; and a plurality of slits (6, 61-67) formed in the rotor core on an outer circumferential side of the magnet retaining holes, the slits being elongated from a vicinity of the permanent magnets to a vicinity of the outer circumference of the rotor core, wherein among the plurality of slits, slits formed in a vicinity of a magnetic pole center of the rotor core are oriented in one direction and slits (61, 67) formed in a vicinity of a pole border portion of the rotor core are oriented in another direction that is different from the direction of the slits formed in the vicinity of the magnetic pole center of the rotor core, characterized in that a width in a radial direction of an outside narrow bridge in the pole border portion is larger than a width in the radial direction of another outside narrow bridge, the outside narrow bridge in the pole border portion being a part of the rotor core on the outer circumferential side of a magnet retaining hole in a vicinity of the pole border portion of rotor, and the another outside narrow bridge being a part of the rotor core on the outer circumferential side of one of the slits (61, 67) formed in the vicinity of the pole border portion. wherein among the plurality of slits, slits formed in a vicinity of a magnetic pole center of the rotor core are oriented in one direction and slits (61, 67) formed in a vicinity of a pole border portion of the rotor core are oriented in another direction that is different from the direction of the slits formed in the vicinity of the magnetic pole center of the rotor core, characterized in that a width in a radial direction of an outside narrow bridge in the pole border portion is larger than a width in the radial direction of another outside narrow bridge, the outside narrow bridge in the pole border portion being a part of the rotor core on the outer circumferential side of a magnet retaining hole in a vicinity of the pole border portion of rotor, and the another outside narrow bridge being a part of the rotor core on the outer circumferential side of one of the slits (61, 67) formed in the vicinity of the pole border portion.