To provide a joint member capable of forming a joint portion that can be easily constructed and has an excellent design and a high waterproof capacity even if it is manufactured at a low cost. A joint member 1 is composed of a hat joiner 10 and a joint cover 20, and the hat joiner 10 is composed of a base plate 11 to be fastened to the body side of building frame and a convex portion 12 protruding from the base plate 11 to the surface side. The joint cover 20 is provided with a joint groove portion 21 that covers a top surface 12c of the convex portion 12 in the course of construction, and a lower edge portion 23 extending from the lower end of the joint groove portion 21 and brought into contact with the surface of an external wall panel 30B in the course of construction. An elastic water proof material 26 is attached to the rear surface of the lower edge portion 23.