NOVELTY - The actuator has a housing (40) whose interior part is provided with a solenoid unit (14). A fixed iron core (50) is arranged at an inner side of the solenoid unit. A rod is made from a magnetic body. A first attraction portion (56) is formed on the fixed iron core, and attracts the rod toward a side of the fixed iron core. A second attraction portion (58) is formed on the fixed iron core, and attracts the movable iron core toward the side of the fixed iron core. A bearing (64) is arranged between the first attraction portion and the second attraction portion.    USE - Electromagnetic actuator for displacing a movable iron core along axial direction by attraction of the movable iron core toward a side of a fixed iron core under excitation action of a solenoid unit for adjusting flow rate of fluid such as hydrogen and oxygen gases, that is utilized in a fuel cell system.    ADVANTAGE - The actuator ensures that multiple stepped portions and multiple recesses are formed on the movable iron core and the fixed iron core so as to increase attractive force along the axial direction with respect to the movable iron core. The stepped portions and the recesses perform guiding function when the movable iron core is arranged along the axial direction. The actuator improves operating precision of the movable iron core and manufacturing precision of the stepped portions and the recesses and reduces manufacturing costs and processing steps for the fixed iron core and the movable iron core. The actuator is simple in structure. The movable iron core can be guided along the axial direction with high precision by the bearing so as to reduce manufacturing cost of the actuator. The movable iron core and a rod portion supported by a guide body are constructed as separate elements so as to reduce constituent parts utilization rate, thus reducing assembly steps. The actuator improves flow of magnetic flux between the movable iron core and a rod element so as to improve magnetic efficiency. The guide bodies are prevented from being influenced by magnetism produced in the solenoid unit, so that magnetic force can be concentrated along the axial direction.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross-sectional view of a valve open state in which a valve element is separated away from a valve seat in an electromagnetic actuator.    Solenoid unit (14)    Housing (40)    Fixed iron core (50)    Attraction portions (56, 58)    Bearing (64)