A medical instrument of the present invention comprises a spiral shaped portion provided at an insertion portion main body, for generating a force at the insertion portion main body to advance/retreat in a subject by a contact with a body wall of the subject, a balloon provided so as to expand radially in a radial direction of the insertion portion main body and capable of contact with the body wall, a suction opening portion provided between the spiral shaped portion and the balloon in the insertion portion main body, and a suction pipeline communicating with the suction opening portion, inserted into the insertion portion main body and connected to a suction pressure controller on a rear end side of the insertion portion main body in the insertion direction.