The ultrasonic probe inside the coelom of this invention has with the frame which includes the interposition section which possesses the medial axis and the attaching part which possesses the longitudinal direction and the ultrasonic unit which is internalized to the interposition section. As for the attaching part, it passes by the center of the profile in the median vicinity of the longitudinal direction of the 1st axis and the frame which match the medial axis of the interposition section possesses with the parallel 2nd axis to the longitudinal direction, the 1st axis from the 2nd axis the offset is done in offset direction in the profile which is vertical to the longitudinal direction of the attaching part. The external surface in the attaching part 1st it is located on the belt which 2nd directs from the axis to offset direction in the profile which is vertical to the longitudinal direction of the attaching part, the external surface part and, 2nd it is located on the belt which is directed to the direction whose 2nd is opposite to offset direction from the axis has with the external surface part, 1st curvature of the external surface part 2nd is smaller than curvature of the external surface part.本発明の体腔内超音波探触子は、中心軸を有する挿入部と、長手方向を有する保持部とを含む筐体と、挿入部に内蔵された超音波ユニットとを備える。保持部は、挿入部の中心軸と一致する第1の軸と、筐体の長手方向の中央近傍における断面の中心を通り、長手方向に平行な第2の軸とを有し、保持部の長手方向に垂直な断面において、第1の軸は第2の軸からオフセット方向にオフセットされている。保持部における外表面は、保持部の長手方向に垂直な断面において、第2の軸からオフセット方向へ向けた線上に位置する第1の外表面部分と、第2の軸からオフセット方向と反対の方向へ向けた線上に位置する第2の外表面部分とを有し、第1の外表面部分の曲率は第2の外表面部分の曲率よりも小さい。
