To simultaneously and sufficiently decrease a plurality of components included in cogging thrust.

A linear motor includes a field yoke 12 provided with a magnet string 14 consisting of a plurality of permanent magnets 13 and an armature 20 that includes an armature core 30 provided with armature coils 21 and is arranged opposite to the magnet string 14 via a magnetic gap. The linear motor 1 travels in a predetermined direction, with either the field yoke 12 or the armature 20 being a movable member 2 and the other being a stator 11. The plurality of permanent magnets 13 of the magnet string 14 are arranged linearly in such a manner that the polarities of adjacent permanent magnets 13 may be alternately different. The armature core 30 includes auxiliary teeth 32A, 32B provided on both ends, respectively, and a plurality of main teeth 31, around which the armature coils 21 are wound, respectively. The auxiliary teeth 32A, 32B have such a shape for a leading end part thereof that the length of the teeth Ht orthogonal to the traveling direction can be changed along the traveling direction.