Affords methods of growing III nitride single crystals of favorable crystallinity with excellent reproducibility, and the III nitride crystals obtained by the growth methods. One method grows a III nitride single crystal (3) inside a crystal-growth vessel (11), the method being characterized in that a porous body formed from a metal carbide, whose porosity is between 0.1% and 70% is employed in at least a portion of the crystal-growth vessel (11). Employing the crystal-growth vessel (11) makes it possible to discharge from 1% to 50% of a source gas (4) inside the crystal-growth vessel (11) via the pores in the porous body to the outside of the crystal-growth vessel (11).