A periodic magnetic field generation device is provided with a field pole of a Halbach array structure in which main pole permanent magnets magnetized in a direction of a generated field and sub pole permanent magnets magnetized in a direction opposite to the direction of magnetic poles of the main pole permanent magnets are alternately disposed linearly or circularly so as to be adjacent to each other. A part of each of the main pole permanent magnets on a side on which the magnetic field is generated is replaced by a soft magnetic member, and a relation between a length A of the soft magnetic member on the side of the generated field along a moving direction and a length B of each main pole permanent magnet on a side of a back yoke along the moving direction is A