A joint structure (1) for a composite member made from a composite material. The joint structure includes a plate for increasing thickness (40a, 40b) adhered to at least one side of the composite member (10). The composite member (10) and a counterpart member (20) are fastened together by inserting and fixing a fastener member (30) into a through-hole (24, 26) formed through the composite member (10), the plate for increasing thickness (40a, 40b), and the counterpart member (20) to be joined to the composite member.