Provided is a rectangular secondary cell enabling seal performance of a gasket to be improved with a simple structure without enlarging a shaft of a terminal. A rectangular secondary cell according to the present invention includes a cell can housing a winding group and having an opening portion, a lid provided with a positive electrode terminal electrically connected to the winding group and closing the opening portion, and a gasket having an interposed portion interposed between the lid and a lower surface of the positive electrode terminal. In the gasket, an external shape of the interposed portion is smaller than an external shape of the lower surface of the positive electrode terminal.