A biodegradable magnesium based metallic material for medical use which is degraded and absorbed in vivo, characterized by comprising a film, which contains magnesium oxide and magnesium hydroxide and is formed on the surface of crystallized magnesium or a magnesium alloy by anodic oxidation. This magnesium based metallic material is capable of exhibiting desired mechanical properties such as strength and ductility at an early stage of implantation without changing the mechanical properties inherent to magnesium or its alloy and also controlling the retention time of the mechanical properties to be short or long in a desired manner.