Abstract: Selenium-containing wastewater is sequentially treated through use of biological treatment means (6), chemical treatment means (12), and filtration means (14). In the biological treatment means (6), raw waste water (16) is subjected to anaerobic biological treatment so as to reduce selenate ions and/or selenite ions (soluble selenium) present in the raw waste water (16) to simple selenium, which is insoluble, to thereby remove the selenate ions and/or the selenite ions in the form of insoluble simple selenium. In the chemical treatment means (12), for example, a metal salt that reacts with soluble selenium to form an insoluble selenium compound is added to water treated by the biological treatment means (6), to thereby remove residual soluble selenium in the form of the insoluble selenium compound. In the filtration means (14), an insoluble substance remaining in water treated by the chemical treatment means (12) is removed through filtration.