An ultrasound catheter includes a transducer unit used for observation of the inside of an organism, observation lumens in which the transducer unit is disposed and which extend in the direction of insertion into the organism, a first guide wire lumen provided substantially in parallel to the observation lumens and on the distal end side in the insertion direction in relation to the transducer unit and through which a guide wire preliminarily brought to the inside of the organism is passed, and a second guide wire lumen provided on an extension line of the first guide wire lumen and on the proximal end side in the insertion direction in relation to the transducer unit and through which the guide wire is passed.