To provide a connection structure between a steel pipe and a foundation of a building structure, which can firmly fix the foundation of a building structure to a foundation steel pipe erected in a ground, and by which the foundation of the building structure is easy in positioning at a work site.

A rectangular base plate 12 is horizontally fixed to a front column 18 of a trestle 61 for solar cell module installation, and bolt members 13, 13... project vertically downward from the base plate 12. Meanwhile, a rectangular joint plate 15 is fixed near front ends of the bolt members 13, 13... so as to be substantially parallel to the base plate 12, and a base end part of an erected foundation steel pipe 1 is inserted through a displacement adjustment hole 26 of the joint plate 15. Then, a fixing plate 16 with a steel pipe insertion hole 22 eccentrically drilled is welded to the foundation steel pipe 1 in a state that the base end part of the foundation steel pipe 1 is inserted through the steel pipe insertion hole 22, and is fixed on a top face of the joint plate 15.