An intracoelomic mobile body for introduction into a body cavity comprising: a capsule body (1112) which has a body (16) to be rotated and can be introduced into the human body and a rotation drive unit (17) which has a rotation shaft (20a) for freely rotating the body to be rotated back and forth. The rotation drive unit is arranged in the capsule body in such a way that a first line (31) obtained by linking the positions of center of gravity of cross-sections formed up to a limit of the formation when the capsule body is cut along a plane perpendicular to the rotation shaft does nor overlap a second line (32) obtained by extending the rotation shaft as the same line.
