Reciprocating engine

A reciprocating engine comprising:

• 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 side thereof that faces the mover;
• an internal space that opens via the aperture portion;
• a wound wire coil that is placed inside the internal space;
• and
• a undercut portion that is formed in the aperture circumferential edge of the aperture portion and that, when viewed in a cross section which includes the axis, is hollowed out from the inner circumferential surface side towards the outside in the radial direction,
• 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, and
• wherein boundary faces between the field magnet portion and the respective restoring magnet portions are each positioned such that, when the mover arrives at a stroke end position where the load on the reciprocating engine is at maximum, the boundary faces reach to a position of the undercut portion.