A fluid purification device includes an inner tube composed of a non-conductive material and an outer tube which is spaced apart from the inner tube by predetermined space S and composed of a non-conductive material, and the tubes are concentrically arranged. A conductive member is attached to apart or entire periphery of the inside of the outer tube to provide an electrode so as to form a device main body. When a voltage is applied to the electrode of the device main body, discharge in the space S is created by using a fluid to be treated W composed of liquid such as water which flows within the inner tube as an earth electrode.This causes a gas such as oxygen or air flowing in the space S to be reacted to generate ozone and mixes the ozone with the fluid to be treated W so as to purify the fluid.