A washing apparatus that easily washes off metal impurities from a porous metal substrate used as an electrode plate core for an alkaline battery. The washing apparatus includes a liquid bath container which holds a solution for washing off the metal impurities. A guide guides movement of the porous metal substrate in the solution held in the liquid bath container. The porous metal substrate is wound into a hoop in a coil-shaped manner, and the guide guides the movement of a sheet portion of the porous metal substrate unwound from the hoop. A winding mechanism winds the sheet portion after being fed through the liquid bath container.