to expose a photosensitive resist on the wafer 150 and so as to suppress an influence of resist thin film interference as shown in fig1 c the focus measuring projection pattern mask 162 has slit shaped marks whose number corresponding to the number of the plural measurement points the beams obtained by illuminating the plural measurement marks undergo optical path synthesis with an optical path combining prism 163 thus the combined beam is projected obliquely on the wafer 150 by a focus mark projection optical system 164 the beam reflected on the wafer 150 surface forms an intermediate imaging point in an optical path dividing prism 166 using a focus light receiving optical system 165 after the beam undergoes optical path division for each measurement point through the optical path dividing prism 166 after that the divided beams are guided to position detection devices 168 for each measurement point by an enlargement detecting optical system 167 arranged for each measurement point with intent to improve a measurement resolving power in this embodiment used as the position detection device 168 is a one dimensional ccd with the measurement direction set to the direction in which the devices are arranged in the perspective view of fig1 b the relationship among the measuring marks the position detection devices 168 and the enlargement detection optical system 167 is shown as viewed from the position detection device 168 in the optical axis direction the position detection devices 168 for each measurement point are arranged in a direction orthogonal to the slit shaped.