Abstract: In a plane motion mechanism, a table is mounted on a top planar surface of a base for movement thereon in plane motion. One end portions of respective first, second and third power transmitting elements adjacent respectively to one ends thereof are wound about an outer peripheral side surface of the table. At least two, first and second, drive units are provided, to which the other ends of the respective first and second power transmitting elements are connected respectively, for applying tension forces respectively to the first and second power transmitting elements. A tension-applying unit, to which the other end of the third power transmitting unit is connected, is provided for applying a tension force to the third power transmitting element. The table may be circular in cross-section and having an outer peripheral side surface.