Joining structure, method of producing same, and wire exterior cover

A method for producing a joining structure, the method comprising:

• a positioning step comprising mating and positioning a bottom surface of a principal surface portion of a first resin sheet comprising a first resin and an end surface portion of a second resin sheet comprising a second resin;
• a welding horn pressing step comprising pressing a leading end of a welding horn against a top surface of the principal surface portion of the first resin sheet while the principal surface portion of the first resin sheet is mated with the end surface portion of the second resin sheet;
• and
• a joint forming step comprising welding the principal surface portion of the first resin sheet and the end surface portion of the second resin sheet, which are mated together, to form a joint using ultrasound emitted from the welding horn
• wherein the first resin is a foamed resin,
• wherein the second resin is a non-foamed or foamed resin, and
• wherein the joint has a weld recess on the top surface and comprises a weld overlay portion formed at an inside corner on the bottom surface by allowing, out of the first and second resins, at least the first resin to melt, flow, and solidify.