A joining method for joining together a first member having a circular hole and a second member having a circular portion fitted into the circular hole, at and around an entire annular joint interface between a circumferential wall of the circular portion and a circumferential wall of the circular hole. The joining method includes: preparing a clamp apparatus having a clamp body and a presser member attached to the clamp body in a manner rotatable about an axis of the circular hole of the first member; and joining the first and second members together at and around the annular joint interface therebetween while clamping the second member by the presser member so as to prevent movement of the second member in relation to the first member and rotating the first and second members about the axis of the circular hole of the first member.