Wastewater such as water discharged by the human body and domestic wastewater which is produced in a confined space, can be treated and recovered with efficiency by using a simple apparatus. Specifically, hardness components of water-to-be-treated are removed with a softening apparatus. Subsequently, electrolysis is performed with a high-temperature high-pressure electrolysis apparatus in order to decompose and remove organic substances, urea, ammonia, and the like. The electrolyzed water is desalinated with a desalination electrodialysis apparatus in order to produce product water and a salt-concentrated liquid. The salt-concentrated liquid is further treated with an acid-alkali production electrodialysis apparatus in order to produce desalinated water, an acid solution, and an alkali solution. The acid solution is used as an agent for regenerating the softening apparatus. The alkali solution is used as an agent for converting the softening apparatus into Na-type. The desalinated water is treated with the desalination electrodialysis apparatus.