A magnet-type rodless cylinder (1) is provided with a guide mechanism having an outer rolling groove (26), an inner rolling groove (29), a cylinder body (32), a pair of connection paths (34) for connecting an area between the outer rolling groove and the inner rolling groove with the cylinder body, and a plurality of steel balls (36) that can roll within an endless circuit (35) formed of the cylinder body, the connection paths and the area between the outer rolling groove and the inner rolling groove, wherein the connection paths (34) are formed at a pair of inner members, i.e. return caps (33), disposed on the inner sides of metal end plates (12) that are attached to the front and rear ends in the sliding direction of a sliding body (4).