According to the present invention, when a person wearing a master device flexes or straightens joints of a finger on which the master device is worn, a control device receives, from the master device, second detection values (DM2j, DM3j) reflecting the bending angles of the joints. The control device also receives a first detection value (DA2j) sent from a magnetic sensor (432j) of a joint motion assist device and a first detection value (DA3j) sent from a magnetic sensor (433j). Then, the control device varies the air pressure within a bellows (342j) so that the absolute value of the difference between the second detection value (DM2j) and the first detection value (DA2j) becomes equal to or less than a prescribed value. The control device further varies the air pressure within a bellows (343j) so that the absolute value of the difference between the second detection value (DM3j) and the first detection value (DA3j) becomes equal to or less than a prescribed value. As a result, the joint motion assist device traces the motion of the finger wearing the master device, thereby making it possible to assist the joint motion properly.
