PROBLEM TO BE SOLVED: To provide a magnesium alloy essentially composed of magnesium, having satisfactory workability and further having high strength (or high tensile strength-high compressive strength).SOLUTION: The magnesium alloy is essentially composed of magnesium, and in the magnesium alloy, the crystal structure thereof has high-angle grain boundaries, and the insides of the crystal grains surrounded by the high-angle grain boundaries is composed of sub-crystal grains, and one kind selected from calcium, tin and yttrium capable of being made into solid solution in magnesium is contained as an additional element. The average crystal grain size of the crystal grains is controlled to ≤10 μm, and the average grain size of the sub-crystal grains is controlled to ≤2 μm. Further, the crystal grains with crystal grain sizes of ≤10 μm occupy 70% or more of the whole body.
