An electricity storage device includes a first electrode, a second electrode, an electricity storage layer, and a p-type semiconductor layer. The electricity storage layer is placed between the first electrode and the second electrode. The electricity storage layer contains a mixture of an insulating material and n-type semiconductor particles. The p-type semiconductor layer is placed between the electricity storage layer and the second electrode. The n-type semiconductor particles contain at least one of a titanium-niobium composite oxide and a titanium-tantalum composite oxide.