Abstract: Along with a reduction in the resistance of a catheter in passing through a valve in an catheter introducer, the hemostatic effect is improved. A main body of the valve is made of a 3-layer structure, and both front and back layers are provided with narrow slits B, B having a crossing at the center, and the interlayer is provided with narrow slit B having a cut closed by contact with the tip of flap 8 protruded from both sides, where the narrow slit in the interlayer is provided as a penetration hole having a round section with the outer periphery in contact with both the sides of the interlayer and in a perpendicular direction to the narrow slits B, B in the back and front layers, as shown in FIG. 8.