ER (electro-rheological) fluids allow direct interfacing between electric signals and fluid power without the need for mechanical moving parts. This study is aimed at achieving the use of ER fluids in micromachines, in particular micro in-pipe mobile machines. In this paper, first, a three-port micro ER valve (φ9.8 mm) is fabricated, which has two pairs of electrodes connected in series. Static characteristics of the micro ER valve are examined. The valve can control a load pressure change of 0.25 MPa at an electric field strength of 5 kV/mm. Secondly, a micro in-pipe mobile machine containing the micro valves, whose diameter and length are φ9.8 mm and 34.5 mm, respectively is fabricated. The micro valves drive bellows microactuators and the in-pipe mobile machine can move in the manner of an inchworm. Performance of the in pipe mobile machine is examined. A maximum average velocity of 0.9 mm/s is obtained without load. An output power of 35μW can be achieved.