To make high-accuracy optical measurement possible by simultaneously lightening the influences of the shapes of the moving surface of a stage and the surface of a slit plate having a slit for detection upon measured results.

In an exposure system, a memory 21 storing the data about the surface shape of the slit plate which is set up nearly perpendicular to the optical axis AX (in Z-direction) of an optical system PL is provided on the stage 18. Consequently, at the time of detecting the optical characteristic of the optical system PL by using a detecting system 59, the difference between the Z-position of the slit and the Z- position of a measuring point can be found accurately, based on the measured results of the Z-position of the measuring point and the data about the surface shape of the slit plate, even when any one of points provided on the surface of the slit plate is selected as the measuring point and the Z-position of the selected point is measured by means of measuring instruments (60a and 60b). Therefore, high-accuracy optical measurement becomes possible by simultaneously lightening the influences of the shapes of the moving surface of the stage 18 and the surface of the slit plate upon the measured results by adjusting the Z-position of the slit plate to a prescribed position based on the difference.