Setting a spatial filter requires repeatedly confirming a scan image through visual inspection by an operator and adjusting the spatial filter. A setting state is also dependent on the operator. Therefore, in the present invention, a scattered light image (beam image) and a diffracted light image (Fourier image) are simultaneously observed, and an intensity profile of the scattered light image (beam image) and an intensity profile of the diffracted light image (Fourier image) are simultaneously monitored. A field of view of a diffracted light image is scanned with only one spatial filter, and a state change with respect to the intensity profiles in the absence of insertion of the spatial filter is detected. A setting condition for a spatial filter is determined on the basis of the detected state change.