The present invention provides that powder is mainly constituted from secondary particles of hydroxyapatite. The secondary particles are obtained by drying a slurry containing primary particles of hydroxyapatite and aggregates thereof and granulating the primary particles and the aggregates. A bulk density of the powder is 0.65 g/mL or more and a specific surface area of the secondary particles is 70 m2/g or more. The powder of the present invention has high strength and is capable of exhibiting superior adsorption capability when it is used for an adsorbent an adsorption apparatus has.