To provide a foundation structure for a solar cell module or solar cell array frame, which allows for easy connection work between a pile and a leg part of the frame, achieving reduction of a construction time.

A foundation structure includes a steel pipe pile body 21 which is embedded in a place for installation of a frame, an adjustment base 30 which is movably attached to the upper end of the steel pipe pile body in the circumferential direction, an elongated adjustment hole 31 formed in the adjustment base 30, and an adjustment and connection member 32 which is movably attached to the elongated adjustment hole 31 in the longitudinal direction and connects a metal fitting arranged at the lower end of the leg part of the frame and the adjustment base 30. The adjustment base 30 is moved along the circumferential direction of the steel pipe pile corresponding to the misalignment between the shaft center of the leg part of the frame and the shaft center of the steel pipe pile body, so as to be fixed to the upper end of the steel pipe pile body. The adjustment and connection member 32 is moved along the longitudinal direction of the adjustment hole 31 corresponding to the misalignment between the shaft center of the leg part of the frame and the shaft center of the steel pipe pile body, such that the metal fitting and the adjustment base 30 are connected through a fixation hole 41 formed in the central part of the metal fitting.