<p>[Problem] To provide an electrochemical device which can excellently maintain connection of a conductive lid to a rigid case. [Solution] A conductive lid (12) has a reinforcing portion (RP) on the inner side of an annular portion to be welded (PP). The portion to be welded (PP) of the conductive lid (12) and the frame portion to be welded (11d) of a rigid case (11) are connected to each other by welding. Stress generated due to an increase of inner pressure of a rigid package (10) due to reflow soldering and the like is relaxed by means of the reinforcing portion (RP) even when the stress is concentrated on the interface between the rigid case (11) and the conductive lid (12).</p>
