Provided is a medical device which can acquire an image throughout a wide range as much as possible. A medical device is provided with a sheath (2) in which a guide wire lumen (211) allowing a guide wire (25) to be inserted therein and an imaging core lumen (26) having an ultrasound transducer (411) that acquires image information inside a living body to be inserted are formed. The medical device includes a rotary shaft (42) that is inserted into the imaging core lumen (26) and is rotatable in order to transmit mechanical drive force to the ultrasound transducer (411). In the sheath (2), a circular portion (261) having constant radii of curvature of the imaging core lumen (26) is formed on a side separated from the guide wire lumen (211), and a non-circular portion (262) having distances from the center point of the circular portion (261) to the inner surface of the imaging core lumen (26) non-uniform and longer than the radius of the circular portion (261) is formed in at least a part of a side close to the guide wire lumen (211).
