A control of a cooperative object-transporting robot which transports an object in cooperation with a man. The robot shares substantially a half of the weight of the object with the man, while the object is kept in a horizontal posture. A force applied to the robot by the object is detected by a force sensor, and based on the signal from the force sensor, a motion instruction is output for the motion components by the rotational force component .tau..sub.1 around the horizontal axis and the translational force component Fx.sub.1 in the horizontal back-and-forth direction, upon setting a gain to reduce the resistance forces of the robot to small values. The translational force component F.sub.y in the direction of the object short axis is constrained so that no translational motion in the direction of the object short axis occurs.