In 2019, EUV lithography technology with a wavelength of 13.5 nm was used for the mass production of semiconductor logic devices with 7 nm node. As with small feature size of electronic circuits in semiconductor device will be required in the future, beyond EUV (BEUV) lithography with exposure wavelength around 6.7 nm is a candidate for the next generation lithography. In BEUV, the developments of high-reflective multilayers, high-sensitive resists, and high-power light sources are critical issues. Thus, we have developed BEUV evaluation tools in NewSUBARU synchrotron light facility. Accurate BEUV reflectometry is significant for the development of high-reflective BEUV multilayer. For the accurate reflectometry, higher-diffraction-order generated from a monochromator should be suppressed. At the BL10 beamline at NewSUBARU, the components of second and third-diffraction-order light are 7% mixed into the BEUV measurement light. Mo transmission filter with a 200-nm-thick was previously used to suppress the higher-order light to 1/10, which was insufficient for target accuracy of 0.1%. We have developed a high-order-light cutting unit consisting of two mirrors with TiO2 coating, which suppressed the high-order light to 1/100.