The Yaizu natural gas field, situated in the Pacific coast of central Japan, is small field with an area of less than 1km2. The total production of dry gas from 13 wells of 100-120 meters in depth, was 950, 000m3 in 1953. Gas reservoir, a gravel bed (G7) in the basal part of the youngest Quarternary deposits, covers a burried basaltic hill and has an elongated dome-shaped structure. Temperature gradient, chlorinity of water and gas-water ratio are high at the top of its structure. Moreover, strange to say, the annual production exceeds its estimated reserves. These phenomena are unusual in the Quarternary gas fields in this country. Therefore, the reservoir must be supplied incessantly with some amount of gas. The origin of supply is probably its underlying Miocene black shale formation which has an imbricated structure. But remarkable heat of the bottom has a different origin.