A distal end of a manipulator having a redundancy is constrained so as to leave one degree of freedom, an attitude of the manipulator is changed into a plurality of attitudes that are allowed by the redundancy by outputting joint position command values from a controller to servomotors that drive links that constitute the manipulator of which the distal end is fixed, and calibration is performed by obtaining parameter deviations of a robot constant of the manipulator on the basis of the joint position command values and actual measured values from rotary encoders, which are respectively provided at the servomotors, after each attitude change.