Abstract: A reciprocating engine includes: an inner stator having an axis; a mover that has a cylindrical shape and is placed coaxially around the inner stator, and that moves reciprocatingly along the axis; and an outer stator that has a cylindrical shape and is placed coaxially around the mover, wherein the outer stator has: an aperture portion that is formed in an inner circumferential surface thereof that faces the mover; an internal space that opens via the aperture portion; and a wound wire coil that is placed inside the internal space, and wherein the mover has: a field magnet portion; and restoring magnet portions that are provided respectively at both end positions along the axis of the field magnet portion.

Abstract: An outer stator is provided in a reciprocating engine together with an inner stator and a mover, that has a cylindrical shape and is placed around the mover coaxially with an axis of the mover, and that forms a magnetic path between itself and the inner stator via a field magnet of the mover, the outer stator includes an aperture portion that is formed in an inner circumferential surface thereof that faces the mover; an internal space that opens via the aperture portion, and in which a wound wire coil is placed; and undercut portions that, in a cross section including the axis, are provided at both end positions along the axis, and that are recessed from the inner circumferential surface towards the outer side in a radial direction.