A non-aqueous electrolyte secondary battery using a transition metal oxide containing solid-solution lithium as a positive electrode; wherein the transition metal oxide containing solid-solution lithium is represented by the compositional formula described below [Chemical Formula 1] Li 1.5 [Ni a M b Mn c [Li] d]O 3, wherein in the formula, Li represents lithium, Ni represents nickel, M represents at least one kind of element selected from the group consisting of silicon, phosphorus and metal elements excluding Ni, Mn and Li, Mn represents manganese, and O represents oxygen, and a, b, c and d satisfy the relationships of 0 < a < 1.4, 0 < b ≤ 0.2, 0 < c < 1.4, 0.1 < d ≤ 0.4, a + b + c + d = 1.5 and 1.1 ≤ [a + b + c] < 1.4, and n, which is the valence of M, is in a range of 4 ≤ n ≤ 6, n being the average value of the valence of each element when M consists of two or more elements, and the transition metal oxide containing solid-solution lithium has a layered structure site and a site which changes to a spinel structure by performing a charge or a charge-discharge in a predetermined electric potential range, and a spinel structure change ratio k of the transition metal oxide containing solid-solution lithium is in a range of 0.25 ≤ k < 1.0 when the spinel structure change ratio is assumed to be 1 in a case where Li 2 MnO 3 of the layered structure in the transition metal oxide containing solid-solution lithium completely changes to LiMn 2 O 4 of the spinel structure; and wherein the predetermined spinel structure change ratio k of the transition metal oxide containing solid-solution lithium is defined according to Mathematical Formula 1 Spinel structure change ratio k = Real capacity of plateau region Theoretical capacity V s due to Li 2 Mn O 3 in solid − solution × Compositional ratio x of Li 2 Mn O 3 in solid − solution, k being obtained by electrochemical pretreatment of performing a charge or a charge-discharge in which the maximum potential of the battery in a predetermined electric potential range is 4.3 V or higher and less than 4.8 V as a conversion to a lithium metal counter electrode, and charge-discharge treatment of performing a charge or a charge-discharge in which the maximum potential of the battery in a predetermined electric potential range is 4.8 V as a conversion to the lithium metal counter electrode. wherein the transition metal oxide containing solid-solution lithium is represented by the compositional formula described below [Chemical Formula 1] Li 1.5 [Ni a M b Mn c [Li] d]O 3, wherein in the formula, Li represents lithium, Ni represents nickel, M represents at least one kind of element selected from the group consisting of silicon, phosphorus and metal elements excluding Ni, Mn and Li, Mn represents manganese, and O represents oxygen, and a, b, c and d satisfy the relationships of 0 < a < 1.4, 0 < b ≤ 0.2, 0 < c < 1.4, 0.1 < d ≤ 0.4, a + b + c + d = 1.5 and 1.1 ≤ [a + b + c] < 1.4, and n, which is the valence of M, is in a range of 4 ≤ n ≤ 6, n being the average value of the valence of each element when M consists of two or more elements, and the transition metal oxide containing solid-solution lithium has a layered structure site and a site which changes to a spinel structure by performing a charge or a charge-discharge in a predetermined electric potential range, and a spinel structure change ratio k of the transition metal oxide containing solid-solution lithium is in a range of 0.25 ≤ k < 1.0 when the spinel structure change ratio is assumed to be 1 in a case where Li 2 MnO 3 of the layered structure in the transition metal oxide containing solid-solution lithium completely changes to LiMn 2 O 4 of the spinel structure; and wherein the predetermined spinel structure change ratio k of the transition metal oxide containing solid-solution lithium is defined according to Mathematical Formula 1 Spinel structure change ratio k = Real capacity of plateau region Theoretical capacity V s due to Li 2 Mn O 3 in solid − solution × Compositional ratio x of Li 2 Mn O 3 in solid − solution, k being obtained by electrochemical pretreatment of performing a charge or a charge-discharge in which the maximum potential of the battery in a predetermined electric potential range is 4.3 V or higher and less than 4.8 V as a conversion to a lithium metal counter electrode, and charge-discharge treatment of performing a charge or a charge-discharge in which the maximum potential of the battery in a predetermined electric potential range is 4.8 V as a conversion to the lithium metal counter electrode.