An input unit enters angular displacements by which drive shafts of a robot arm are to be turned as teaching data into a control unit. The control unit converts the input angular displacements into position-attitude data, namely, converted commands, indicating a position of the free end of the robot arm and an attitude of the robot in a rectangular coordinate system through forward conversion. The control unit corrects the position-attitude data on the basis of inherent errors in the robot to provide corrected position-attitude data. The control unit converts the corrected position-attitude data into corrected angular displacements through inverse conversion and gives the corrected angular displacements to an actuator included in the robot. The inherent errors in the robot include mechanismic errors resulting from machining errors and assembling errors, installation errors and errors in the origins of axes.