The Horiba energy-dispersive XRF microscanner is an instrument designed for nondestructive, high-resolution, rapid, semiquantitative chemical mapping under ordinary atmospheric conditions. However, its application to quantitative analysis has not yet been attempted. In this study we developed a nondestructive, rapid, high-resolution, quantitative analytical method for fine-grained rocks using this instrument. Average concentrations and elemental mapping images of a small square region (0.5 mm × 0.5 mm to 100 mm × 100 mm) can be obtained for major elements (Mg, Al, Si, K, Ca, Ti, Mn, Fe) within 100 seconds per measurement. High-resolution, continuous measurements of slabbed fine-grained sedimentary rock samples are easily achieved. A stratigraphic interval of 1 m can be measured with 1 cm resolution within 10 hours, which is several times faster than the conventional X-ray fluorescence method.