A magnesium-based alloy powder is made of a magnesium-based alloy that contains 0.2 mass % to 5 mass % of calcium, wherein the magnesium-based alloy powder has an average particle diameter of 100 μm to 1,500 μm, wherein the magnesium-based alloy powder has a particle average aspect ratio of 0.5 to 1, wherein the magnesium-based alloy powder has an apparent density of 0.2 g/cm3 to 1.2 g/cm3, and wherein the mean value of hardness variation index values obtained by dividing the difference of the maximum value and the minimum value of micro Vickers hardnesses taken at 10 measurement points in a particle cross section by the maximum value is 0.3 or less.