The scanning magneto-optical Kerr effect (MOKE) method was developed by using a soft x-ray free-electron laser to visualize magnetic microstructures with element-selectivity. For focusing optics of soft x-rays, an ellipsoidal mirror with an achromatic property was utilized to obtain resonant MOKE spectra for various elements with a simple experimental setup. We performed a scanning MOKE experiment at Fe M-edge with a spatial resolution of 7 mu m. This system is readily applicable to ultrafast MOKE experiments combined with a synchronized optical laser for spintronics research.