Conventional clonoscope is semiflexible tube that should be manipulated by operator for inspection and treatment. Therefore, it sometimes causes pain for the patient and even perforation to the wall of colon if a surgeon is not well trained. For safe colonoscopy, self-propelling robots with inchworm locomotion are studied. But, inchworm locomotion has some problems in adaptiveness to the variation of colon diameter. In this paper, we propose novel locomotive mechanism which can move in the colon without any external assistance. It has several cams that have constant phase difference each other and located along the centerline of the mechanism. This mechanism could realize the robotic endoscope which has continuous and smooth thrust force.