Recently, colonoscopy has become much more important with increasing number of colonic diseases. However, the inspection time depends on the doctor's skill strongly. In this research, we aim at development of a tube type rubber pneumatic actuator for assisting insertion of a large intestine endoscope. This actuator can be wound around endoscopes in a spiral configuration. In previous paper, two types of actuator were developed and some experiments were conducted. However, there were drawbacks, one actuator could not generate enough output, and the other one was difficult to mount on endoscopes. In this paper, novel actuator has been designed by non-linear FEM (Finite Element Method) to realize high mountability and drivability. The actuator is configured with three air chambers, and by applying pneumatic pressure to each chamber in proper sequence, elliptical motion of the actuator has been confirmed by non-linear FEM analysis and experiments using motion capture system. Moreover the self propelling velocity and the traction force have been increased compared to previous actuators and effectiveness of this actuator has been confirmed from the phantom experiments.