A lithium ion secondary battery includes: (a) a positive electrode plate comprising an active material part and a current collector carrying the active material part, the active material part comprising a positive electrode active material capable of absorbing or desorbing a lithium ion during charge and discharge; (b) a negative electrode plate comprising an active material part and a current collector carrying the active material part, the active material part comprising a negative electrode active material capable of absorbing or desorbing a lithium ion during charge and discharge; (c) a separator interposed between the positive and negative electrode plates; (d) an electrolyte; and (e) a battery case accommodating the positive and negative electrode plates, the separator, and the electrolyte. The positive and negative electrode plates are wound with the separator interposed therebetween, thereby to form an electrode plate assembly. The electrode plate assembly is so configured that each lengthwise edge of the positive electrode current collector is positioned on an outer side of each lengthwise edge of the negative electrode active material part.