Abstract: Provided are a concrete foundation structure capable of firmly fixing a precast concrete foundation to a ground, and a method for constructing the concrete foundation structure. A concrete foundation structure 10 includes a precast concrete foundation 16 having a projecting portion 30 embedded in a ground G. An anchor plate 20 is placed inside an excavation hole 18 formed in the ground G, and the precast concrete foundation 16 and the anchor plate 20 are connected by a connecting member 22. In the excavation hole 18, a backfill portion 24 is formed of a backfill material 94 including a solidifying material and soil. A filler layer 26 is formed of a filler 96 containing a solidifying material between the precast concrete foundation 16 and the backfill portion 24. The precast concrete foundation 16 has a through-hole 42 through which the connecting member 22 is inserted, and the filler 96 forming the filler layer 26 is filled through the through-hole 42.