To provide a steel pipe connecting structure for inexpensively providing the connection having strength equal to respective steel pipes to be connected with a simple structure.

Joint pieces 11a and 11b are arranged in arrangement extended in the shaft direction of the respective steel pipes in respective joining end parts of the cylindrical steel pipes 10a and 10b to be mutually connected in the extending direction. Both joint pieces are positioned and mutually superposed on the inner peripheral surface side and the outer peripheral surface side of the steel pipes. On contact planes of both joint pieces, a recessed groove 13 turned in the steel pipe peripheral direction is provided in its one, and a projection strip 14 fitted to the recessed groove 13 is integrally provided in the other. Both mutual joint pieces are fixed by a bolt 17 in a state of fitting the recessed groove and the projection strip.