A lithium ion secondary battery comprising a battery element obtained by alternately stacking a plurality of positive electrodes having layers of a positive electrode active material formed on both sides of positive current collectors and a plurality of negative electrodes having layers of a negative electrode active material formed on both sides of negative current collectors through separators in such a way that the positive electrode active material layers face the negative electrode active material layers, the battery element impregnated with liquid electrolyte and held by a laminate case (23; 31, 32), the lithium ion secondary battery having the following configuration characterized in that: the positive electrode active material has an average particle size of 3 to 10 μm and a total thickness of the positive electrode active material layers formed on both sides of the positive current collector is 30 to 110 μm, the negative electrode active material has an average particle size of 5 to 10 μm and a total thickness of the negative electrode active material layers formed on both sides of the negative current collector is 30 to 100 μm, and terminals (6, 7) of the positive electrode and the negative electrode are led out to the outer edge part with the terminals (6, 7) separated from each other and the positive electrode terminal and the negative electrode terminal respectively satisfy the formula: B / A ≥ 0.57 where A is a width of a region of the active material region perpendicular to the direction of current and B is a width of the electrode terminal perpendicular to the direction of current. a battery element obtained by alternately stacking a plurality of positive electrodes having layers of a positive electrode active material formed on both sides of positive current collectors and a plurality of negative electrodes having layers of a negative electrode active material formed on both sides of negative current collectors through separators in such a way that the positive electrode active material layers face the negative electrode active material layers, the battery element impregnated with liquid electrolyte and held by a laminate case (23; 31, 32), the lithium ion secondary battery having the following configuration characterized in that: the positive electrode active material has an average particle size of 3 to 10 μm and a total thickness of the positive electrode active material layers formed on both sides of the positive current collector is 30 to 110 μm, the negative electrode active material has an average particle size of 5 to 10 μm and a total thickness of the negative electrode active material layers formed on both sides of the negative current collector is 30 to 100 μm, and terminals (6, 7) of the positive electrode and the negative electrode are led out to the outer edge part with the terminals (6, 7) separated from each other and the positive electrode terminal and the negative electrode terminal respectively satisfy the formula: B / A ≥ 0.57 the positive electrode active material has an average particle size of 3 to 10 μm and a total thickness of the positive electrode active material layers formed on both sides of the positive current collector is 30 to 110 μm, the negative electrode active material has an average particle size of 5 to 10 μm and a total thickness of the negative electrode active material layers formed on both sides of the negative current collector is 30 to 100 μm, and terminals (6, 7) of the positive electrode and the negative electrode are led out to the outer edge part with the terminals (6, 7) separated from each other and the positive electrode terminal and the negative electrode terminal respectively satisfy the formula: B / A ≥ 0.57 where A is a width of a region of the active material region perpendicular to the direction of current and B is a width of the electrode terminal perpendicular to the direction of current.