Provided is a medical device including: a first elongated body； an electrode that is fixed to the annular expansion portion of the first elongated body； a second elongated body that has a distal portion and a proximal portion, a first lumen communicating from the distal portion to the proximal portion, and a second lumen parallel to the first lumen at the distal portion； and an ultrasound element that is configured to move inside the first lumen of the second elongated body in an axial direction, in which the first elongated body is inserted into the second lumen, and the linear portion of the first elongated body is positioned in a direction orthogonal to the axial direction of the ultrasound element, and the ultrasound element receives ultrasound reflected from the first elongated body and ultrasound reflected from a body-cavity around the second elongated body.
