An electrochemical device according to the present disclosure is provided with: a first stack which contains an oxide ion conductor as an electrolyte, and generates hydrogen and oxygen by decomposing water vapor; a second stack which contains a proton conductor as an electrolyte, and separates hydrogen from a mixed gas of the hydrogen generated by the first stack and the water vapor that is not decomposed by the first stack; and a heat insulating material which covers the first stack and the second stack.