A movable iron core linear actuator of which moving element (2, 202, 302) is made to reciprocate, the linear actuator comprising a magnetic circuit which includes: an iron core (20, 220, 320) which constitutes the moving element (2, 202, 302); a stator core (10, 210, 310) which includes a facing portion (10c, 110c, 210c, 310c) which faces the iron core (20, 220, 320); a pair of permanent magnets (12, 12a, 12b, 212a, 212b, 312a, 312b) disposed in a facing portion (10c, 110c, 210c, 310c) along the reciprocating direction, the pair of permanent magnets (12, 12a, 12b, 212a, 212b, 312a, 312b) having inverted magnetic poles at their surfaces which face the iron core (20, 220, 320); and a coil wound around the stator core (10, 210, 310), the magnetic circuit causing, via the magnetic flux produced by energization of the coil, the moving element (2, 202, 302) to reciprocate by weakening the magnetic flux produced in the magnet situated in a necessary direction between the pair of permanent magnets (12, 12a, 12b, 212a, 212b, 312a, 312b), and strengthening the magnetic flux produced in the other magnet, and when the coil is being energized, spring force of the magnetic spring which varies in accordance with a relative position of the moving element (2, 202, 302) with respect to the stator core (10, 210, 310) being superimposed on electromagnetic driving force produced by the energization of the coil and applied to the moving element (2, 202, 302) by the magnetic flux produced by the permanent magnets (12, 12a, 12b, 212a, 212b, 312a, 312b), and when the coil is not energized, the pair of the permanent magnets (12, 12a, 12b, 212a, 212b, 312a, 312b) forms a loop-shaped magnetic flux path which starts at one permanent magnet (12, 12a, 212a, 312a) passes through the iron core (20, 220, 320), the other permanent magnet (12, 12b, 212b, 312b) and the stator core (10, 210, 310) and returns to one permanent magnet (12, 12a, 212a, 312a), wherein a space portion (30, 130, 230) having low magnetic permeability compared with the stator core (10, 210, 310) is formed to constitute a magnetic spring adjustment portion (3, 303) which changes magnetic flux distribution, characterized by the space portion (30, 130, 230) being formed in a state in which a part of the facing portion (10c, 110c, 210c, 310c) is removed in an area, which is in the middle of the loop-shaped magnetic flux path, between a part of the facing portion (10c, 110c, 210c, 310c) of the stator core (10, 210, 310) and the permanent magnet and, by this magnetic spring adjustment portion (3, 303), the magnetic spring characteristic which is the relationship between the relative position of the moving element (2, 202, 302) with respect to the stator core (10, 210, 310) and the spring force of the magnetic spring is changed compared with a case in which no space portion (30, 130, 230) is formed. an iron core (20, 220, 320) which constitutes the moving element (2, 202, 302); a stator core (10, 210, 310) which includes a facing portion (10c, 110c, 210c, 310c) which faces the iron core (20, 220, 320); a pair of permanent magnets (12, 12a, 12b, 212a, 212b, 312a, 312b) disposed in a facing portion (10c, 110c, 210c, 310c) along the reciprocating direction, the pair of permanent magnets (12, 12a, 12b, 212a, 212b, 312a, 312b) having inverted magnetic poles at their surfaces which face the iron core (20, 220, 320); and a coil wound around the stator core (10, 210, 310), the magnetic circuit causing, via the magnetic flux produced by energization of the coil, the moving element (2, 202, 302) to reciprocate by weakening the magnetic flux produced in the magnet situated in a necessary direction between the pair of permanent magnets (12, 12a, 12b, 212a, 212b, 312a, 312b), and strengthening the magnetic flux produced in the other magnet, and when the coil is being energized, spring force of the magnetic spring which varies in accordance with a relative position of the moving element (2, 202, 302) with respect to the stator core (10, 210, 310) being superimposed on electromagnetic driving force produced by the energization of the coil and applied to the moving element (2, 202, 302) by the magnetic flux produced by the permanent magnets (12, 12a, 12b, 212a, 212b, 312a, 312b), and when the coil is not energized, the pair of the permanent magnets (12, 12a, 12b, 212a, 212b, 312a, 312b) forms a loop-shaped magnetic flux path which starts at one permanent magnet (12, 12a, 212a, 312a) passes through the iron core (20, 220, 320), the other permanent magnet (12, 12b, 212b, 312b) and the stator core (10, 210, 310) and returns to one permanent magnet (12, 12a, 212a, 312a), wherein a space portion (30, 130, 230) having low magnetic permeability compared with the stator core (10, 210, 310) is formed to constitute a magnetic spring adjustment portion (3, 303) which changes magnetic flux distribution, characterized by the space portion (30, 130, 230) being formed in a state in which a part of the facing portion (10c, 110c, 210c, 310c) is removed in an area, which is in the middle of the loop-shaped magnetic flux path, between a part of the facing portion (10c, 110c, 210c, 310c) of the stator core (10, 210, 310) and the permanent magnet and, by this magnetic spring adjustment portion (3, 303), the magnetic spring characteristic which is the relationship between the relative position of the moving element (2, 202, 302) with respect to the stator core (10, 210, 310) and the spring force of the magnetic spring is changed compared with a case in which no space portion (30, 130, 230) is formed.