An electrochemical system includes a first stack, a first tank for storing high-pressure gas output from the first stack, a check valve disposed in a flow path connecting the first stack and the first tank, a first pressure sensor and a second pressure sensor connected respectively to the upstream and the downstream of the check valve, and a control unit. The control unit determines that an electrolyte membrane has been damaged when the pressure difference between the upstream and the downstream of the check valve exceeds a predetermined pressure.