PURPOSE: To obtain a filler composed of hydroxyapatite(HPA) which is porous and whose durability is excellent by a method wherein slurry which contains an HPA particle A synthesized in a specific temperature range and an HPA particle B synthesized in a higher temperature region is granulated and fired.

CONSTITUTION: A granulated substance is prepared from slurry which contains an HPA particle A synthesized in a temperature region of less than 800°C and an HPA particle B synthesized in a high temperature region of 800°C or higher and in which the mixture ratio of the particle B is 30 to 60% of the total weight. The granulated substance is fired at 800°C or higher and formed. When the particle A is heated at its firing temperature of 800°C or higher, its volume is contracted due to a sintering reaction. On the other hand, the particle B is a thermally stable single crystal or polycrystal whose volume is not contracted by the same heating. Consequently, when, e.g. the porous particle B having a pore whose diameter is larger than that of the particle A is used, the particle A which has crept into the pore of the particle B is crystallized at the inside and the outside of the pore of the particle when it is fired, a firm bond is produced in such a way that the particle B is taken into due to the sintering reaction, and it is possible to obtain a filler whose pore volume is kept and whose mechanical strength is large.