The body of an automatic water combination faucet has, as separate parts, an outer cylinder with the cylindrical wall thereof having assembling hole portions for assembling connectors connected to the hot water, water and combination water lines and an inner cylinder housing accommodating a mixing valve unit. The inner cylinder housing is formed by casting or the like, and has, as integral and continuous parts, a main portion accommodating the mixing valve unit, a passage-defining portion in the form of a line for leading hot water to the main portion, and a passage-defining portion in the form of a duct line for leading out combination water. A separate cap which surrounds an adjustment screw unit of the mixing valve unit is engagedly coupled to the main portion. The passage-defining portions of the inner cylinder housing have respective open ends, which can be aligned, with the inner cylinder housing fitted in the outer cylinder, to the hot water lead-in and combination water lead-out assembling hole portions in an abutting relation thereto. The peripheral wall of the main portion has an opening for leading in water.