An electrode unit is for use in a power transmitting device or a power receiving device of a wireless power transmission system based on an electric field coupling method. The electrode unit includes; a first group of electrodes including a plurality of first electrodes to which a first voltage is applied when power is transmitted; and a second group of electrodes including a plurality of second electrodes to which a second voltage is applied when power is transmitted, wherein the second voltage has a phase that is different from a phase of the first voltage by a value greater than 90 degrees and less than 270 degrees. The plurality of first electrodes and the plurality of second electrodes are arranged in a first direction along an electrode installation surface. At least two of the plurality of first electrodes and at least two of the plurality of second electrodes are arranged alternating with each other in the first direction.