The optimum waste treatment was examined for the system of a garbage bio-gasification along with an incineration. Inventories of the environmental loading and costs of the life cycle are calculated for the combination system of the garbage bio-gasification facility and the gasification fusion furnace. The life cycle cost and the environmental loading are greatly dependent on applications of the generating bio-gas and purifying methods of the waste water from the facility. The desirable system is that garbage is sorted in home and is treated with the bio-gasification facility and the bio-gas is introduced and combined to the power generation of the incinerator, leading to the high efficient power generation, and that the waste water from the bio-gas facility is run in the public sewerage after the simple purification in the system.