An electrochemical apparatus includes: a reformer that produces a first hydrogen-containing gas by reforming a raw material; a combustor that heats the reformer; an electrochemical device that includes an anode and a cathode, the electrochemical device operating by using the first hydrogen-containing gas supplied to the anode; a first flow rate controller that controls a flow rate of the first hydrogen-containing gas supplied to the anode and a flow rate of a second hydrogen-containing gas supplied from a supply source, the second hydrogen-containing gas being different from the first hydrogen-containing gas; a second flow rate controller that controls a flow rate at which an anode-off gas exhausted from the anode is recycled to the anode and a flow rate at which the anode-off gas is supplied to the combustor; and a controller that controls the first flow rate controller and the second flow rate controller.