The Research Center for Photovoltaics investigates calibration and evaluation method of photovoltaics (PV). In the field of calibration, we contribute to a sound spread and promotion of PV as the top of traceability through calibration of a reference cell that is a transferred standard of the traceability. The calibration value is utilized as the key comparison reference value of World PV Scale. We have developed a new calibration system for a primary reference cell which was composed of a highly-collimated solar simulator, a wide-band spectroradiometer and a spectral responsivity measurement equipment, etc. The ray parallelism of the simulator is less than 1.2 degree in double angle. Thus we have achieved the direct traceability to the World Radiometric Reference (solar irradiance scale) on indoor calibration by the simulator and an absolute cavity radiometer.