To provide joint construction of a casing tube with high strength capable of bearing the increase of force-fit force without being deformed for a powerful excavator by all-casing method, etc.

Joint construction of a casing tube is so constituted that joint metal fixtures consisting of male and female types are welded to both longitudinal ends of double pipe construction built up of an internal pipe and an outer pipe of steel materials, and a large number of casing tubes are jointed to execute excavation. In that case, the number of lock pin holes 4a as an integer obtained by dividing an overall circumferential angle of 360 degrees along the circumferential direction of the joint metal fixtures of male and female types is opened at equal intervals, and power transfer pin holes 4b are opened at equal intervals among the lock pin holes 4a. Then, the number of lock pin holes 4a is limited to 8, 10 or 12 pieces, and the number of power transfer pin holes 4b is limited to 4 or 6 pieces.