Link 1, turning about fixed axis F, is connected by turning pair B to slider 3. Slider 3 moves along axis CD of the extension of slider 4 which moves along fixed guides p-p. Sliders 7 and 2, connected together by turning pair E, move along axes Da and Fb of links 5 and 1. Link 5 moves in slider 6 which turns about fixed axis A. Centre F is placed at the focus of a conic section, centre A is placed on the given directrix d-d at its intersection wi th the perpendicular drawn from point F, and the condition G͞F:G͞A=F͞B:G͞A=e is complied with, where e is the given eccentricity. Then, when link 1 turns about axis F, point E describes a conic section. Point E describes an ellipse when e<1, a parabola when e=1 and a hyperbola when e>1.