The invention provides a battery module and a manufacturing method of the battery module. Provided is the battery module in which a stacked body (142) of a plurality of flat batteries (144A to 144D) stacked on one another is housed. The battery module includes the flat batteries, an output terminal, a metal container, insulating plates and an insulating cover (170). Each of the flat batteries (144A to 144D) includes a power-generating element, an exterior package member for sealing the power-generating element, and electrode terminals led out from the exterior package member. The output terminal is used to provide a parallel or series connection between the electrode terminals of the plurality of flat batteries (144A to 144D) and to output power therefrom. The metal container is used to house the stacked body. The insulating plates are disposed to hold the electrode terminals of the flat batteries (144A to 144D) therebetween in such a way to insulate the electrode terminals from one another, and also include window portions through which the electrode terminals are exposed for the connection. The insulating cover (170) is disposed in such a way to cover the window portions of the insulating plates (160A, 160E) located in the outermost layers.