A medical device includes a sheath having a guide wire lumen allowing a guide wire to be inserted therein and an imaging core lumen configured to have an ultrasound transducer inserted therein that acquires image information inside a living body. The medical device includes a rotary shaft that is inserted into the imaging core lumen and is rotatable in order to transmit mechanical drive force to the ultrasound transducer. In the sheath, a circular portion having a constant radii of curvature of the imaging core lumen is formed on a side separated from the guide wire lumen, and a non-circular portion having distances from the center point of the circular portion to the inner surface of the imaging core lumen non-uniform and longer than the radius of the circular portion is formed in at least a part of a side close to the guide wire lumen.
