renewing process should be initiated or not is not limited to the one described above it may be one that includes at least the former of the output of the acceleration sensor 4 and the offset value furthermore while the offset measuring and renewing process is carried out while the base table is being seated it may be carried out while the base table is being floated moreover although in the embodiments described above the number of actuators is not specified it may be one or more generally actuators are mounted on a supporting leg of the base table if there are three supporting legs extending in a vertical direction regarding the base table position control system a three axis control system may be provided including a z axis vertical driving axis translational control system a rotational control system about the x axis and a rotational control system about the y axis this is also the case with the vibration control system as regards the supporting legs for supporting the base table they are not limited to vertical ones supporting legs adapted to drive the base table in a horizontal direction may be mounted for example by providing an air spring in a horizontal direction swinging motion of the base table in the horizontal direction can be suppressed effectively alternatively electromagnetic actuators for driving the base table in a horizontal.