To provide a phosphate-based dental investment material which can used for metal and press ceramic and especially can impart the lubricity to the surface of a press ceramic, and a phosphate-based dental investment material which can be subjected to a flash heating for press ceramic, can obtain sufficient the hardening expansion, and can easily remove the investment material after press molding. A phosphate-based dental investment material of the present invention comprising a powder material and a liquid material, wherein the powder material contains (a) magnesium oxide: 5 to 20 wt.%； (b) ammonium dihydrogenphosphate: 8 to 25 wt.% and the liquid material contains (c) aqueous solution including a cation-treated colloidal silica.
