The invention relates to mechanical engineering, can be used in various engineering fields and makes it possible to improve the reliability and service life of a device having small radial overall dimensions. The inventive rodless piston internal combustion engine comprises a body (1) provided with covers (25, 26) in which a drive shaft (23) is mounted on bearings (24) and interacts with a gear unit (18) (G). Cam rollers (15) placed in hubs (17 G 18) are brought into contact with thrust blocks (10) (T) of pistons (8) which are provided with support washers (9) (SW). A lock ring is located between the (T) (10) and (SW) (9).