KAGRA, the gravitational wave telescope located in japan, has started the Observing run called O4 with LIGO and Virgo.
For accurately extracting physical information from gravitational wave signals obtained by gravitational wave telescopes, the calibration of the telescopes becomes crucial.
Calibration groups in LIGO, Virgo and KAGRA use the same calibration method called the photon calibrator (Pcal) method, actuating end-mirrors of an interferometer, by using laser radiation pressure, to generate calibrated reference signals for calibration.
The system relies on the power meter to measure the laser.
For the accurate and precise reference signal generation, we use integrating sphere type power meter that allow precise and accurate measurements.

In this proceedings, we report the angular and polarization dependence of integrating spheres and consider the effect on the uncertainly of the KAGRA Pcal system.