The purpose of the present invention is to provide an electrode which is used as a liquid flow-through device electrode and in which liquid flow-through resistance is reduced and the utilization efficiency of carbon fiber is enhanced. Another object of the present invention is to provide a redox flow battery having excellent charge-discharge performance by use of the electrode which is used for the liquid flow-through device. The present invention provides an electrode for a liquid flow-through device, the electrode essentially consisting of a carbon fiber nonwoven fabric, having a thickness of more than 0.40 mm, and having a through-hole disposed therein, or a non-through-hole disposed on one surface or both surfaces of the electrode.