A medical device includes a cover member and a holding member. The cover member includes: an accommodating section so provided as to be able to accommodate either one of a right lung and a left lung of a living body and freely deformable according to inflation and deflation of a lung which is accommodated in the state of accommodating the lung therein and an opening through which the lung is introduced into the accommodating section. The holding member is provided at the opening of the cover member, deforms the aperture shape of the opening by having its oppositely located arbitrary portions brought closer to or away from each other, and so functions that the aperture area of the opening is thereby held constant before and after the deformation.
