A calibration method in which, a rotation angle calculation device calculates a rotation angle based on a detection signal of a sensor, transmits rotation angle data indicating the rotation angle to a calibration device, and transmits time difference data relating to a time difference after having captured the detection signal until transmitting the rotation angle data to the calibration device, and in which the calibration device measures a rotation angle, clocks a measurement time at which the rotation angle is measured and a transmission time of transmitting or receiving the rotation angle data, and acquires calibration data of the rotation angle data by comparing the rotation angle measured at a time obtained by going back in time from the transmission time by the time difference after having captured the detection signal until transmitting the rotation angle data and the rotation angle data with each other.