A method for producing an electrode plate group unit for a lithium-ion capacitor, whereby a collector member and a pole plate are reliably welded together, and the resistance of the welded part is low, is provided. A lithium-ion capacitor is also provided. An uncoated section (25) of a positive electrode plate (9) and an uncoated section (33) of a negative electrode plate (11) are configured so as to protrude further to the outside than separators (13, 15) in the opposite direction, and an electrode plate group (5) is configured in such a manner as to be wound in a spiral in a cross-section as the core of an axis core (7). A metal lithium support member (17) is disposed on the negative electrode plate (11) in such a manner that a wound layer of the metal lithium support member (17) is positioned in the central area of the electrode plate group (5) in the radial direction. With a negative electrode collector (45) mounted on the uncoated section (33), welding is carried out using a direct light-focusing semiconductor laser device that continuously generates a laser beam to produce the electrode plate group unit for the lithium-ion capacitor (2). A lithium-ion capacitor (1) is obtained by housing the electrode plate group unit for the lithium-ion capacitor (2) in a container (3).