A positive electrode active material for an electric device, the positive electrode active material comprising: a first active material composed of a transition metal oxide represented by compositional formula 1: Li 1.5 [NiaCobMnc[Li]d]O3.. where, in the formula 1, Li is lithium, Ni is nickel, Co is cobalt, Mn is manganese, O is oxygen, a, b, c and d satisfy relationships: 0.15 ≤ d ≤ 0.25; a+b+c+d = 1.5; and 1.25 ≤ a+b+c ≤ 1.35; the first active material includes: a layered structure region that is changed to a spinel structure by performing charge or charge/discharge in a potential range of 4.3V or more to 4.8V or less; and a layered structure region that is not changed to the spinel structure thereby; and a second active material composed of a spinel-type transition metal oxide represented by compositional formula 2 and having a crystal structure belonging to a space group Fd-3m: LiMa' Mn2-a' O4... where, in the formula 2, Li is lithium, M is at least one selected from the group consisting of aluminum, magnesium and chromium, O is oxygen, and a' satisfies a relationship: 0 ≤ a' < 0.5, wherein a content ratio of the first active material and the second active material satisfies, in a mass ratio, a relationship represented by expression 3: 100: 0 < MA: MB < 0: 100 where, in the expression 3, MA is a mass of the first active material, and MB is a mass of the second active material wherein a BET specific surface of the first active material is 0.8 m2/g or more to 10.0 m 2 /g or less, wherein a 50%-penetration particle diameter of the first active material is 20 μm or less, and wherein a spinel structure change ratio is 0.25 or more to less than 1.0, wherein the spinel structure change ratio is determined as outlined in the description. a first active material composed of a transition metal oxide represented by compositional formula 1: Li 1.5 [NiaCobMnc[Li]d]O3.. where, in the formula 1, Li is lithium, Ni is nickel, Co is cobalt, Mn is manganese, O is oxygen, a, b, c and d satisfy relationships: 0.15 ≤ d ≤ 0.25; a+b+c+d = 1.5; and 1.25 ≤ a+b+c ≤ 1.35; the first active material includes: a layered structure region that is changed to a spinel structure by performing charge or charge/discharge in a potential range of 4.3V or more to 4.8V or less; and a layered structure region that is not changed to the spinel structure thereby; and a second active material composed of a spinel-type transition metal oxide represented by compositional formula 2 and having a crystal structure belonging to a space group Fd-3m: LiMa' Mn2-a' O4... where, in the formula 2, Li is lithium, M is at least one selected from the group consisting of aluminum, magnesium and chromium, O is oxygen, and a' satisfies a relationship: 0 ≤ a' < 0.5, wherein a content ratio of the first active material and the second active material satisfies, in a mass ratio, a relationship represented by expression 3: 100: 0 < MA: MB < 0: 100 where, in the expression 3, MA is a mass of the first active material, and MB is a mass of the second active material wherein a BET specific surface of the first active material is 0.8 m2/g or more to 10.0 m 2 /g or less, wherein a 50%-penetration particle diameter of the first active material is 20 μm or less, and wherein a spinel structure change ratio is 0.25 or more to less than 1.0, wherein the spinel structure change ratio is determined as outlined in the description.