A non-destructive method for measuring an active area of an active material, the method comprising: manufacturing three kinds of electrodes, i.e. a first electrode coated with an electrode mixture containing both the electrode active material and a conductive material, a second electrode coated with an electrode mixture containing the electrode active material as its main component and not containing the conductive material, and a third electrode coated with the electrode mixture containing no active material and containing the conductive material as its main component; manufacturing three monocells (200, 300), wherein in each monocell the same electrodes are used, wherein each monocell (200, 300) is a symmetrical cell comprising a counter electrode (240, 340), a working electrode (230, 330) with a separator interposed therebetween, and an electrolyte, in which the first electrode and the first electrode, the second electrode and the second electrode, the third electrode and the third electrode are the working and counter electrodes of the first, second and third monocells respectively; measuring, by cyclic voltammetry, a capacitance C total, C 2 and C 3 respectively of the first, second and third electrodes used in the monocells; and calculating the active area of the electrode active material by a following formula 1, wherein A A. M = C total − C CNT ∗ A CNT / C A. M, in which A A.M denotes the active area (m 2) of the electrode active material in the electrode mixture coated on the first electrode, A CNT denotes the surface area (m 2) of the conductive material in the electrode mixture coated on the first electrode, wherein A CNT is obtained by multiplying the weight of the conductive material used for the first electrode with the Brunauer-Emmett-Teller value of the used conductive material, Ctotai denotes the capacitance of the first electrode, wherein Ctotai is obtained by measuring the capacitance of the first electrode, C CNT denotes the capacitance per unit surface area of the conductive material (F/m 2), wherein C CNT is a value obtained by dividing the capacitance measurement value C 3 of the third electrode by the surface area A 3 of the third electrode, and C A.M denotes the capacitance per unit surface area of the electrode active material (F/m 2), wherein C A.M is obtained by dividing the capacitance measurement value C 2 of the second electrode by a surface area A 2 of the second electrode. manufacturing three kinds of electrodes, i.e. a first electrode coated with an electrode mixture containing both the electrode active material and a conductive material, a second electrode coated with an electrode mixture containing the electrode active material as its main component and not containing the conductive material, and a third electrode coated with the electrode mixture containing no active material and containing the conductive material as its main component; manufacturing three monocells (200, 300), wherein in each monocell the same electrodes are used, wherein each monocell (200, 300) is a symmetrical cell comprising a counter electrode (240, 340), a working electrode (230, 330) with a separator interposed therebetween, and an electrolyte, in which the first electrode and the first electrode, the second electrode and the second electrode, the third electrode and the third electrode are the working and counter electrodes of the first, second and third monocells respectively; measuring, by cyclic voltammetry, a capacitance C total, C 2 and C 3 respectively of the first, second and third electrodes used in the monocells; and calculating the active area of the electrode active material by a following formula 1, wherein A A. M = C total − C CNT ∗ A CNT / C A. M, in which A A.M denotes the active area (m 2) of the electrode active material in the electrode mixture coated on the first electrode, A CNT denotes the surface area (m 2) of the conductive material in the electrode mixture coated on the first electrode, wherein A CNT is obtained by multiplying the weight of the conductive material used for the first electrode with the Brunauer-Emmett-Teller value of the used conductive material, Ctotai denotes the capacitance of the first electrode, wherein Ctotai is obtained by measuring the capacitance of the first electrode, C CNT denotes the capacitance per unit surface area of the conductive material (F/m 2), wherein C CNT is a value obtained by dividing the capacitance measurement value C 3 of the third electrode by the surface area A 3 of the third electrode, and C A.M denotes the capacitance per unit surface area of the electrode active material (F/m 2), wherein C A.M is obtained by dividing the capacitance measurement value C 2 of the second electrode by a surface area A 2 of the second electrode.