<p>The purpose of the present invention is to provide a water treatment device and a water treatment method that are capable of ensuring mechanical strength and water permeability as well as further improving water treatment efficiency and economy. The water treatment method uses a water treatment device comprising a membrane module using hollow fiber membranes having a separating function in both surfaces thereof; and includes alternating between total filtration water treatment and backwashing. The water treatment device has an independent structure having an outer diameter of 3.6-10 mm, an SDR value being the ratio between the outer diameter and the thickness of 5.8-34, and an inner diameter of at least 3.2 mm.</p>
