Provided is a method of manufacturing a positive electrode material for an electrical storage device, the positive electrode material for an electrical storage device including a positive electrode active material represented toy the general formula Nax(Fe1−aMa)yP2Oz, where M represents at least one kind of transition metal element selected from the group consisting of Cr, Mn, Co, and Ni, x satisfies 1.2≤x≤2.8, y satisfies 0.95≤y≤1.6, a satisfies 0≤a≤0.9, and z satisfies 7≤z≤8, the method including a step of firing an oxide material serving as a raw material at from 400° C. to 610° C. in a reducing atmosphere.