A medical instrument includes a first tube body and a second tube body joined to the first tube body by being inserted in the lumen of the first tube body. The second tube body is more rigid than the first tube body. The medical instrument includes a coating layer made of a biocompatible material disposed on the inner peripheral surfaces of the first and second tube bodies. The inner peripheral surface of the second tube body is radially inward of the inner peripheral surface of the first tube body to create a level difference portion. The thickness of the part of the coating layer which coats the level difference portion is larger than the thickness of the level difference portion.