An introducer assembly is composed of an introducer sheath and a dilator which have been previously integrated with each other to permit the hemostatic valve to exhibit its hemostatic function over an extended period of time without significantly adversely affecting the inherent function of the dilator tube. The introducer assembly includes a dilator tube passing through a passage of a hemostatic valve. The introducer assembly has a deforming member arranged between the hemostatic valve and a cap. As the cap is pushed toward the proximal end surface of a sheath hub for engagement with the sheath hub, the cap presses the hemostatic valve and applies a compressive force to the hemostatic valve in such a direction as to close the passage.
