A reduction electrode of an embodiment includes a metal base material and a plurality of metal nanowires provided on the metal base material. The plurality of metal nanowires include metal nanowires whose average height of contour curve of surface is 20 nm or less for 50% or more in a number ratio. The plurality of metal nanowires are formed by reducing a plurality of metal oxides each having a nanowire shape formed on the metal base material by an electrochemical reduction method. A reduction process of the metal oxides includes a first process of passing a current under a constant current condition where an absolute value is 5 mA/cm2 or more through the plurality of metal oxides, and a second process of passing a current under a constant potential condition through the plurality of metal oxides.