Belle II, as the upgrade of Belle, is aiming at searching for New Physics with 40 times higher luminosity. In order to cope with such a high luminosity, pure CsI scintillation crystals whose scintillation time is around 30 nanoseconds have been proposed. And silicon avalanche photodiodes, making up for the low light yield of pure CsI, are considered as photosensors. The application of the innovative WLS which perfectly matches the emission spectrum of pure CsI and quantum efficiency of APD, maximizes the light collection. With the help of cosmic rays, the equivalent noise energy of the counter is measured.