A diagnostic imaging catheter is disclosed which includes a drive shaft, of which a distal portion is provided with a signal transmitting and receiving unit, and which can be rotated; a sheath including a lumen into which the drive shaft is inserted such that the drive shaft can be moved forward and backward; a communicating hole which is provided in a distal portion of the sheath, and through which the inside and the outside of the sheath communicate with each other; and a valve body capable of opening and closing the communicating hole. The valve body is configured to be capable of switching between a closed state in which the communicating hole is covered and blocked with the valve body and an open state which the valve body enters by being moved to the outside of the sheath from the closed state, and in which the communicating hole is open.