PROBLEM TO BE SOLVED: To provide a power assist device not requiring a large installation space at low cost.SOLUTION: In a power assist device 1000, one end of an air muscle 110 for generating assist force for an object is supported by a frame 130 to be suspended. A load cell unit 106 for detecting force applied to the air muscle is provided, for example, between a transport unit 100 connected with an object 10 to be transported and the other end of the air muscle. A detection unit 124 detects a change in length of the air muscle. A control unit 200 controls the assist force generated by the air muscle depending on a detection result of the load cell unit. The control unit controls pressure applied to the air muscle for generating the assist force by a reverse model of a drive force model representing a predetermined relation of the assist force with respect to a contraction ratio of the air muscle.
