A pipe joint structure includes a plurality of fluid flow path portions, a socket connected to the fluid flow path portions, a connection plate disposed to abut against the socket, a plurality of pipes connected to each other by the connection plate, and a seal member disposed between the plurality of pipes and the socket. The socket includes a connection portion that is located to cover an edge of the connection plate and to fix the plurality of pipes to the plurality of fluid flow path portions. The pipe joint structure can be suitably used for a heat exchanger.