The medical device (1) of the present invention includes an elongated long part (2) that can be inserted into one of two cavities separated by a body wall, and a distal end of the long part (2). Provided in the seat part (3), a seat part (3) provided to cover the surface of the body wall, an attachment part (6) provided around the circumference of the sheet part (3) and in close contact with the surface of the body wall Informing the operator that the body wall has been incised from the other cavity side to the one cavity side based on the fact that the sheet part (3) is exposed from the incision site of the body wall to the other cavity side. Part (5).本発明の医療用デバイス（１）は、体壁によって隔てられた２つの腔の内、一方の腔内に挿入可能な細長い長尺部（２）と、該長尺部（２）の先端に設けられ体壁の表面を覆うシート部（３）と、該シート部（３）の周囲に全周にわたって設けられ体壁の表面に密着する取付部（６）と、シート部（３）に設けられ、体壁が他方の腔側から一方の腔側まで切開されたことを、体壁の切開部位からシート部（３）が他方の腔側に露出することに基づいて術者に報知する報知部（５）とを備える。
