To provide a method for coating the surface of biometal material with hydroxyapatite in a temperature range causing no dissolution of the hydroxyapatite, and to provide a method for joining the biometal with the hydroxyapatite.

The biometal is coated/joined with the hydroxyapatite through the use of property to perform polarization by the electric field of the hydroxyapatite. The biometal is brought into contact with the hydroxyapatite and a DC voltage is applied as a positive pole onto the biometal. Alkaline earth metal ions, alkaline metal ions, and protons contained in apatite are moved to a negative pole side by the force of the electric force which is generated by applying the voltage. An alkaline earth metal ion-depleted layer, etc., is formed in the neighborhood of the hydroxyapatite on a boundary surface between the biometal and the hydroxyapatite. The depleted layer excessively contains hydroxide ions or oxygen ions to be strongly negatively charged. A strong electrostatic attraction force is generated between the biometal and the hydroxyapatite by the electrostatic attraction force between the negative charge and a positive charge which is induced on the front surface of the biometal material. Thus, the biometal tightly adheres on the hydroxyapatite. Besides, permanent joint is achieved by the mutual diffusion of the biometal and the hydroxyapatite.