PURPOSE: To produce a small type cylinder which can be prevented from rotating by forming the section of a cylinder tube into a polygon in the cylinder whose driven magnet row is followingly slided by magnetic action as a driving magnet row slides between the cylinder tubes.

CONSTITUTION: The inside and the outside of a cylinder 1 are provided with a driving magnet row 2 insertedly fitted slidably in an axial direction and a driven magnet row 3 followed by magnetic action as the driving magnet row 2 slides respectively. A cylinder tube 4 is polygonal in its section, and each component for forming the driving magnet row 2 and the driven magnet row 3 has a shape corresponding to the section of the cylinder tube. Thus the driven magnet row 3 of a rodloss cylinder can be prevented from rotating without providing another member to miniaturize the cylinder.