An electrochemical device comprises an electrode matrix including a multilayer structure composed of a positive electrode, a negative electrode, and a first separator, and first and second dummy electrodes electrically connected to the positive and negative electrodes, respectively. The first and second dummy electrodes have respective opposing parts opposing each other through a second separator at an outer peripheral part of the electrode matrix. One or each of the first and second dummy electrodes has a resistance control layer at least on a side where the opposing parts oppose each other. The resistance control layer has such a resistance value that an estimated internal short circuit current between the first and second dummy electrodes is equivalent to 0.09 C to 1.00 C. The first and second dummy electrodes are adapted to short-circuit each other at a lower temperature than the positive and negative electrodes do.