In the medical field, a medical instrument may be used as a blood circuit constituting an extracorporeal circulation circuit or the like in some cases. The medical instrument includes a tube body (hereinafter, referred to as a first tube body) which is flexible and a tube body (hereinafter, referred to as a second tube body) such as a connector, which has a rigidity higher than that of the first tube body (i.e., the second tube body is more rigid than the first tube body) and is fitted in the first tube body. When the medical instrument is used, blood circulates through a lumen of the first tube body and a lumen of the second tube body. Therefore, an inner peripheral surface of each tube body is provided with a coating layer having biocompatibility (i.e., a biocompatible coating is applied to the inner surface of the first and second tube bodies).
The coating layer is made of various types of materials which are available. For example, Japanese Patent Application Publication No. H04-152952 discloses a medical instrument that uses a synthetic polymer having biocompatibility and antithrombotic.