A positive electrode material for lithium-ion secondary batteries, which includes a carbon-coated positive electrode active material, characterized in that the carbon-coated positive electrode active material comprises primary particles, secondary particles which are agglomerates of the primary particles, and a carbon film, wherein the primary particles and the secondary particles are coated with the carbon film; the primary particles consists of a positive electrode active material in which a crystal strain of the positive electrode active material, which is calculated by X-ray diffraction measurement, is 0.01% or higher and 0.1% or lower; a ratio (B/A) of a crystallite diameter B (nm) of the positive electrode active material to an average primary particle diameter A (nm) of the carbon-coated positive electrode active material is 0.9 or higher and 1.5 or lower, wherein the average primary particle diameter A is calculated from a specific surface area of the carbon-coated positive electrode active material, and the specific surface area is a value obtained by a BET method, the positive electrode material is represented by general formula LiFePO 4; wherein, using a diffraction peak in a range of 2θ=15° to 75° obtained by the X-ray diffraction of the positive electrode material, the crystal strain and the crystallite diameter B of the positive electrode active material are estimated from a slope and an intercept of a line according to Expression using Williamson-Hall method, β cos θ = Cε sin θ + K λ / L (in the expression, θ represents a Bragg angle; β represents an integral width which corresponds to a width of a rectangle having the same height and the same area of the diffraction peak; ε represents the strain; L represents the crystallite diameter B; λ represents a radiation wavelength, and C and K represent constants of 4 and 0.9); and wherein the average primary particle diameter A of the carbon-coated positive electrode active material is calculated from Expression, primary Particle Diameter A nm = 6 / True Specific Gravity g / m 3 of Carbon-Coated Positive Electroade Active Material × BET specific surface area m 2 / g of Carbon-Coated Positive Electrode Active Material × 10 9 wherein the true specific gravity of the carbon-coated positive electrode active material in the Expression is set to 3600000 g/m 3. the carbon-coated positive electrode active material comprises primary particles, secondary particles which are agglomerates of the primary particles, and a carbon film, wherein the primary particles and the secondary particles are coated with the carbon film; the primary particles consists of a positive electrode active material in which a crystal strain of the positive electrode active material, which is calculated by X-ray diffraction measurement, is 0.01% or higher and 0.1% or lower; a ratio (B/A) of a crystallite diameter B (nm) of the positive electrode active material to an average primary particle diameter A (nm) of the carbon-coated positive electrode active material is 0.9 or higher and 1.5 or lower, wherein the average primary particle diameter A is calculated from a specific surface area of the carbon-coated positive electrode active material, and the specific surface area is a value obtained by a BET method, the positive electrode material is represented by general formula LiFePO 4; wherein, using a diffraction peak in a range of 2θ=15° to 75° obtained by the X-ray diffraction of the positive electrode material, the crystal strain and the crystallite diameter B of the positive electrode active material are estimated from a slope and an intercept of a line according to Expression using Williamson-Hall method, β cos θ = Cε sin θ + K λ / L (in the expression, θ represents a Bragg angle; β represents an integral width which corresponds to a width of a rectangle having the same height and the same area of the diffraction peak; ε represents the strain; L represents the crystallite diameter B; λ represents a radiation wavelength, and C and K represent constants of 4 and 0.9); and wherein the average primary particle diameter A of the carbon-coated positive electrode active material is calculated from Expression, primary Particle Diameter A nm = 6 / True Specific Gravity g / m 3 of Carbon-Coated Positive Electroade Active Material × BET specific surface area m 2 / g of Carbon-Coated Positive Electrode Active Material × 10 9 wherein the true specific gravity of the carbon-coated positive electrode active material in the Expression is set to 3600000 g/m 3.