A substrate processing device capable of stabilizing an etching amount of a metal film provided on a substrate is provided. The substrate processing device includes a first container, a second container and a control unit. The first container stores a first liquid in which an acid solution containing phosphoric acid and water are mixed. The first liquid is capable of etching a metal film provided on a substrate. The second container stores a second liquid containing water. The control unit controls supply of the second liquid from the second container to the first container such that a water concentration of the first liquid increases over time corresponding to change in a concentration of the phosphoric acid in the first liquid.