Tumor-induced osteomalacia (TIO) is a rare paraneoplastic disease characterized by hypophosphatemia and skeletal undermineralization. Overproduction of fibroblast growth factor 23( FGF23) from the responsible tumor is reported to be a causative factor. Removing the tumor is the only effective treatment for TIO, but identifying the tumor is sometimes difficult. A 43-year-old man complained of heel pain 4 years earlier, and the pain gradually expanded to the whole body. As a blood test showed the elevation of the serum FGF23 level and hypophosphatemia, he was diagnosed with FGF23-related hypophosphatemia. Chest computed tomography (CT) showed a 10-mm nodule in the right chest wall. Venous sampling for FGF23 revealed considerable elevation of the FGF23 level in the right subclavian vein. Therefore, a chest wall tumor was suspected as the tumor responsible for TIO, and surgical resection was performed. After surgery, hypophosphatemia improved within several days, and the FGF23 level also normalized.