Abstract: The present disclosure relates to an energy storage device comprising: a housing for accommodating an electrolyte; an electrode element accommodated inside the housing; a case coupled to one side of the housing; and an electrode terminal inserted into the case so as to be electrically connected to the electrode element, wherein the case comprises: a base part having a through-hole into which the electrode terminal is inserted; and a sealing part coupled to the base part so as to seal the space between the base part and the electrode terminal, and the sealing part includes a terminal sealing member located at the through-hole so as to come into close contact with the electrode terminal, thereby sealing the space between the base part and the electrode terminal.