To provide an apparatus for producing a substrate, in which a crucible can be uniformly heated by decreasing a temperature gradient in the periphery of the crucible compared to a conventional method in the production of a gallium nitride substrate for producing a gallium nitride crystal on a seed substrate by supplying nitrogen gas to a melt containing gallium and sodium.

The apparatus (A) for producing a substrate is equipped with a first vessel (inner vessel) 12 having a heater 12a attached inside, and a crucible 14 housed inside the first vessel 12, and produces a crystal substrate on a seed substrate 20 to be immersed in a melt 30 in the crucible 14 by heating the crucible 14 with the heater 12a of the first vessel 12. The apparatus is also equipped with a heat insulating vessel 13 that is housed inside the first vessel 12 and houses the crucible 14.