PURPOSE: To estimate the load weight and perform proper feedforward control as to a body attached additionally to a controlled system.

CONSTITUTION: The load weight is estimated as to a tool fitted to the tip of the arm of a six-axes robot. The robot begins to be moved first according to a proper operation program. Adaptive control is performed for 4th-6th axes (step S1). At adaptive control convergence time (step S2), estimated moments gr4-gr6 of the 4th-6th axes and the estimated load inertia J5 of the 5th axis are stored (step S3). An additional weight estimation equation is solved as to m6, x6g, y6g, and z6g by using those data and the respective axis values θ3-θ6 of the robot and parameters m5, s5z, l5z, J5m, g, etc., and the result is stored (step S4). When the robot reaches an end point position (step S5), the robot is stopped and the processing ends. The found parameters of the load weight are used to calculated feedforward terms when subsequent feedforward control is performed.