Provided is a joined body comprising a first joined member, a second joined member, and a joining layer that joins the first joined member and the second joined member, wherein the first joined member and the second joined member are each independently one selected from the group consisting of a metal member, a polyamide resin member, and a polyolefin resin member, and the joining layer is a layer formed of a resin composition having a co-continuous phase including a continuous phase A farmed of the polyamide resin and a continuous phase B formed of the polyolefin resin and has a dispersed domain a distributed in the continuous phase A, a finely dispersed subdomain a′ distributed in the dispersed domain a, a dispersed domain b distributed in the continuous phase B, and a finely dispersed subdomain b′ distributed in the dispersed domain b.