The present invention, with a simplified construction, prevents or suppresses flow of blood into a catheter sheath caused by negative pressure being created in the catheter sheath due to a pullback process during scanning. According to the present invention, a cylinder which contains a liquid is provided on a pullback portion and the cylinder is connected to the catheter. A plunger inside the cylinder is moved by the force of a linear drive portion due to the pullback portion to pressurize the liquid inside the cylinder. This causes the liquid inside the cylinder to also pressurize the liquid inside the catheter, which avoids or makes it difficult for negative pressure to be created inside the catheter sheath, thereby preventing or suppressing flow of blood therein.
