For the purpose of using soil as a heat sink and heat source, we conducted a heat exchange experiment employing a steel pile used for building foundations as a heat exchanger with the soil. The steel pile had a 400-mm external diameter and was installed vertically to a depth of 20 m. The quantity of heat exchanged with the soil and variations in the water temperature in a steel pile were investigated. The heat exchanged with the soil per day was 210 MJ as a heat sink, and 113-150 MJ as a heat source during a short-term experiment. Numerical calculations were performed by using a three-dimensional finite difference equation to predict the water temperature and the quantity of heat exchanged with the soil. The calculation results agreed well with the experimental results, which showed that the calculation method could predict variations in the water temperature and the quantity of heat exchanged with the soil. Then the quantity of heat collected with the steel pile in a long-term operation was estimated by using a calculation method based on the short-term experiment. It was estimated to be about one-third of the amount of heat collected in the short-term experiment.