There is disclosed a water treatment device capable of improving the treatment efficiency of for-treatment water and passing the for-treatment water once to sufficiently treat the water without repeatedly circulating the water, and the water treatment device includes a water passing first electrode arranged in the channel of the for-treatment water, a conductive fiber positioned on the downstream side of this first electrode and energized by the first electrode, a water passing second electrode positioned on the downstream side of this conductive fiber and forming a pair with the first electrode, an insulating porous spacer interposed between this second electrode and the conductive fiber, and a supply section which supplies voltages to both of the electrodes.