To provide a water collection device that can be hardly affected by bubbles when a permeate is taken out.

The water collection device having water collecting pipes 34A, 34B that collect the permeate from a plurality of membrane elements 30 immersed in a liquid to be treated and are immersed and disposed in the treating liquid, wherein a header pipe 42 that collects the permeating liquid from a plurality of the pipes 34A, 34B is disposed above a liquid level of the liquid to be treated with a smaller channel cross-section area of a downstream pipe 46 that sends the permeating liquid from the pipe 42 than the sum of those of each insertion pipe 40A, 40B that allows the permeating water to flow into the pipe 42.