To provide a foundation structure that can prevent termites from entering the inside of a heat insulator and decrease labor and time required for constructing the foundation structure.SOLUTION: A termite prevention sheet attached heat insulator 15 has a main body 41 and a protruding piece 42 that protrudes from the main body 41. The main body 41 has a heat insulator and a first termite prevention sheet and a second termite prevention sheet that are attached to the heat insulator. The protruding piece 42 is formed by attaching an end of the first termite prevention sheet and an end of the second termite prevention sheet. The termite prevention sheet attached heat insulator 15 is installed so that a main surface of the main body 41 abuts against an external wall surface 17 of an upstanding section 13 of a continuous footing 11. The protruding piece 42 of the termite prevention sheet attached heat insulator 15 is attached to the external wall surface 17 of the upstanding section 13 using a silicone-based adhesive 18. Termites are prevented from entering the inside of a foundation structure 10 from between the main body 41 of the termite prevention sheet attached heat insulator 15 and the upstanding section 13.SELECTED DRAWING: Figure 5