A long-proportional-stroke force motor which outputs force proportional to the exciting current. The motor has a magnetic circuit wherein a non-magnetic spacer is positioned axially between a magnetic guide and a magnetic sleeve. An armature moves within a central opening defined by the guide, the spacer and the sleeve. An end portion of the guide, adjacent to the spacer, has a sectional profile through a stepped surface facing radially outward and the corners of the steps define a curve which satisfies the following expressions: ⅆ Y ⅆ X > 0 , ⁢ ⅆ 2 ⁢ Y ⅆ X 2 > 0 , where X is a coordinate on an X-axis corresponding to a central axis of the guide; wherein the armature is moved in a direction along the X-axis by application of exciting current to a coil surrounding the guide, spacer and sleeve; and Y is a coordinate on an axis orthogonal to the X-axis.