This paper reports the development of thin straight fibers type artificial muscles. The straight fiber types of artificial muscle have greater contraction ratio and power and a longer lifetime than McKibben types. And the thin straight type artificial muscle is a micro miniaturization of the straight type artificial muscle that is examined ahead in this laboratory. It has the outside diameter of 1.2 millimeters and the inside diameter of 0.5 millimeters. Therefore it can work in a limited space. For example, it is expected that the muscles would be used for the direction control in the point part of industrial endoscopes.