A method of manufacturing an electrode group unit for lithium ion capacitor that allows reliable welding between a current collecting member and an electrode and that provides a welded portion with a low resistance is provided. A lithium ion capacitor is also provided. An unapplied portion 25 of a positive electrode 9 and an unapplied portion 33 of a negative electrode 11 are disposed to project outside of separators 13, 15 in directions opposite to each other. The resulting assembly is wound into a swirling shape in cross section about an axial core 7 to form an electrode group 5. A lithium metal support member 17 is disposed on the negative electrode 11 such that a layer in which the lithium metal support member 17 is wound is located in a radially middle region of the electrode group 5. A negative current collecting member 45 is placed on the unapplied portion 33, and welding is performed using a direct-collecting semiconductor laser device that continuously generates laser light to manufacture an electrode group unit 2 for lithium ion capacitor. The electrode group unit 2 for lithium ion capacitor is housed in a container 3 to obtain a lithium ion capacitor 1.