Layer stack object formation method, including forming layer of powder material containing calcium phosphate and delivering hardening liquid to predetermined region of the layer to harden the region,wherein these steps are repeated,wherein 1) powder material satisfies A) or B), and hardened product of powder material has hydroxyapatite (HAp) transformation rate of ≦1%: A) organic compound having phosphate or carboxyl group is imparted over surface of calcium phosphate powder, and organic compound imparting amount is ≦10,000 ppm and B) powder material further contains powder made of organic compound having phosphate or carboxyl group, and organic compound mixing amount to calcium phosphate powder is ≦50% by mass, orwherein 2) hardening liquid contains at least organic compound having phosphate or carboxyl group, acid value of organic compound is ≧0.45 gKOH/g, and content of organic compound to whole amount of hardening liquid is ≧20% by mass.
