of the system of fig4 only two actuators 15 15a and 15b are illustrated in the drawing for simplification however at least three or more actuators are necessary to provide movability in rotational directions about x and y axes respectively denoted at 16 is a control box for controlling the stage as a whole denoted at 17 is a focus control box for detecting the level and tilt of an exposure region on the wafer 19 on the basis of a detection signal from the surface position detecting means 13 denoted at 18 is a reference table wherein the relation between changes in the level and tilt of the wafer 19 with respect to an image plane and the stepwise motion amounts and x y coordinates having been determined beforehand are stored denoted at 111 is a light source such as a white light lamp for example and denoted at 112 is a collimator lens for transforming the light from the light source 111 into parallel light having an approximately uniform sectional intensity distribution denoted at 113 is a slit member of prism like shape having plural openings e g five pinholes denoted at 114 is a light projecting lens system which comprises a dual telecentric system and which serves.