The present invention relates to a method and an apparatus for calibrating a transformation matrix [B] of a force sensor, in which: a force sensor (12) is attached between a wrist portion (10c) and a hand portion (13) of a robot (10); a standard work (weight) (31) whose weight and position of a center of gravity are known is attached or held to the hand portion (13); each driving source (M) of the robot (10) is made operative in response to commands from a control unit (40) and thereby sequentially changing the posture of the force sensor (12) attached to the robot (10); the control unit (40) obtains a force (F) consisting of a force and a moment due to an arithmetic operation from the posture and position information of the force sensor (12) which is detected on the basis of signals from encoders (PE) to detect an operation amount of each operating element of the robot (10) and from the weights and the positions of the centers of gravity of the standard work (31) and the hand portion (13) and the like inputted as data; the control unit (40) receives a strain voltage (V) detected from the force sensor (12); the control unit (40) calculates the transformation matrix [B] of the force sensor (12) from the force (F) consisting of the force and moment derived and from the strain voltage (V) received in accordance with a predetermined arithmetic logic equation and then stores the transformation matrix [B] into memory means (42); and then the transformation matrix [B] of the force sensor (12) is calibrated.