To provide a method for producing a nitride crystal, with which reuse of a reaction vessel is made possible by preventing breakage of the reaction vessel, and with which a high-quality crystal is obtained, in growing the nitride crystal with an ammonothermal method.

After a raw material and an ammonia solvent are filled in the reaction vessel and sealed therein, the reaction vessel is set up in a pressure-tight vessel having a valve, and further after a second solvent is filled in the void between the pressure-tight vessel and the reaction vessel and the pressure-tight vessel is tightly sealed, the nitride crystal is grown in a supercritical and/or a subcritical ammonia atmosphere in the reaction vessel. In this case, the pressure difference between the outside and the inside of the reaction vessel is adjusted so as to be small via the valve.