An electrochemical device has an electrochemical cell provided with an electrolyte having proton conductivity, an anode provided on one side of the electrolyte, and a cathode provided on the other side of the electrolyte. The electrochemical device is configured so that a solution containing water, an artificial synthetic resin, and an acid is supplied to the anode. The electrochemical device is configured so that an oxygen-containing gas is supplied to the cathode and connecting a load between the anode and the cathode. The electrochemical device is configured so that the inert gas is supplied to the cathode and connecting the voltage application unit between the anode and the cathode.