The output of a gravitational wave telescope is a voltage signal which needs to be calibrated to get the strain signal h(t). This signal h(t) can then be used to derive various parameters of
the gravitational wave sources. Any uncertainty in the calibration is directly transferred to these parameters. Therefore, absolute calibration of gravitation wave detectors using a precise reference (known) signal is essential.

Currently, KAGRA uses Photon Calibrator (PCAL) to generate reference signals for calibration. PCAL injects a power-modulated laser onto the test mass to calibrate the absolute displacement
of the mirror using radiation pressure. Hence, the absolute calibration of KAGRA is limited to 3% by the absolute laser power measurement uncertainty due to the deviation in the laser power standards.

KAGRA proposed a new method combining PCAL with Gravity Field Calibrator (GCAL) to reduce the calibration uncertainty. GCAL modulates the test mass using a dynamic gravitational field generated by rotating multipole masses. Since the injected force by GCAL depends on the gravitational constant, mass, distance, rotation frequency, and radius, calibration uncertainty in the sub-percent region can be achieved.

In this presentation, we will report on the progress of the development of the gravity field calibrator and our future plans.