NOVELTY - An upper yoke (34a), which covers one end face of excitation coil (32), has first facing surface (41) that faces the outer circumferential face of small diameter section of movable element (36) and second facing surface (42) that the faces one end face of small diameter section. A lower yoke (34b), which covers the other end face of excitation coil to magnetically connect with the upper yoke, has third facing surface (43) that faces the outer circumferential face of large diameter section (40) of movable element, and fourth facing surface (44) that faces one end face of large diameter section.    USE - Used as actuator for pump (claimed) used for, e.g., feeding air and fuel to fuel cells, medical devices, cooling notebook-size computers.    ADVANTAGE - Stable thrust generation range is extended, broad-ranging thrust characteristics is gained and controllability is improved since outer circumferential face of the large diameter section, which is located at the outermost position with respect to the guide pipe, faces the third facing surface of lower yoke. Gaps between the facing surfaces of lower yoke and small diameter section of movable element and gaps between the facing surfaces of lower yoke and large diameter section of movable element are highly narrowed, and permeance between facing surfaces is increased so that great thrust is gained since deformation of the guide pipe, which is caused by winding the coil wire on guide pipe and shaping the coil is prevented, and clearance between the inner diameter of guide pipe and outer diameter of the small diameter section of movable element is previously minimized. Reduces weight of the portion of movable element so that thrust is further increased since concave section is formed in the other end face of large diameter section of movable element and caved toward the one end face. Prevents vibration caused by the contact of large diameter section and lower yoke since end face of the large diameter section contacts the rubber cushion when movable element is moved toward one end side. Enough thrust and superior pumping ability is gained by low electric power even if pump is downsized by employing the solenoid.    DETAILED DESCRIPTION - Excitation coil is previously wound and put on the outer circumferential face of guide pipe (37). Guide pipe is made of synthetic resin and integrally molded with the excitation coil.    DESCRIPTION OF DRAWING(S) - The figure shows the sectional view of a pump using the solenoid.    Excitation coil (32)    Upper yoke (34a)    Lower yoke (34b)    Movable element (36)    Guide pipe (37)    Large diameter section (40)    First facing surface (41)    Second facing surface (42)    Third facing surface (43)    Fourth facing surface (44)