To provide a means which has an evaluation index numerically expressed on whether or not an electrode plate can be wound around without cutting and which contributes to suppression of variations in an electrode group caused by cutting of the electrode plates and improvement in productivity, when the electrode group is constructed by winding around centered on the axial center a positive electrode plate, a negative electrode plate, and a separator compressed in a prescribed thickness in spiral shape.

Both ends of an electrode plate 1 cut-out in rectangular shape are pinched by a clip jig 2 and a round rod 7 is inserted in an annular portion on the opposite side to fix to a round rod support body, and the clip jig 2 is raised until the electrode plate 1 is fractured, and the load at the time of fracture is measured, thereby, the strength of the electrode plate is numerically expressed. By defining the ratio of the thickness of the current collector of the positive electrode plate and thickness of the mixture paint, an electrode group with stable quality is supplied by suppressing cutting of the electrode plate, and a non-aqueous secondary battery with little variations in battery capacity and showing an excellent life characteristics are supplied.