Abstract: A water treatment apparatus includes: a mixing element having a mixing tank in which water is mixed with a flocculant added thereto; a flocculation element having a cylindrical flocculation tank into which the water discharged from the mixing element is introduced, and in which the water is kept unexposed to the atmosphere, a for-treatment water inlet which introduces the water to be treated into the flocculation tank from a lower part of the flocculation tank in a tangential direction so as to produce a swirl flow, and a for-treatment water outlet discharging the water to be treated from the upper part of the flocculation tank; and a solid-liquid separation element into which the water to be treated after discharge from the flocculation element is introduced from the flocculation element without being exposed to the atmosphere, and in which the water to be treated is subjected to solid-liquid separation.