The present invention provides a non-volatile storage element and a non-volatile storage device that use a ferroelectric material, can be embedded in advanced CMOS logic, and are excellent in low power consumption and high reliability, and especially in data rewriting endurance. The non-volatile storage element at least has a first conductive layer, a second conductive layer, and a ferroelectric layer that is constituted by a metal oxide and is located between the first and second conductive layers, and a buffer layer having oxygen ion conductivity is present between the ferroelectric layer and the first conductive layer and/or the second conductive layer. Further, the non-volatile storage element has an interfacial layer constituted by a single layer film or a multiple layer film between the first conductive layer and the ferroelectric layer, the interfacial layer as a whole has permittivity higher than that of a silicon oxide, and the interfacial layer is present between the first conductive layer and the buffer layer when the buffer layer is present between the first conductive layer and the ferroelectric layer. The non-volatile storage device is at least provided with a control circuit, and a memory cell array formed by two-dimensionally or three-dimensionally arranging ferroelectric storage elements having low power consumption. The ferroelectric layer, which can be scaled to 10 nm or less, is manufactured at a low temperature of 400˚C or less and is subjected to low-temperature thermal annealing at 400˚C or less after formation of the buffer layer to improve reliability.