A manufacturing method for a joined body, includes: bringing a first member and a second member into contact with each other, at least one of the first member and the second member being made of thermoplastic resin, and the second member having a recessed portion on a joining surface to be joined to the first member; and welding the first member and the second member together, including welding a contact portion of the first member and the second member by melting the thermoplastic resin by frictional heat generated in the contact portion by relative movement of the first member and the second member, in a state in which the first member and the second member are in contact with each other.