To produce a group III nitride crystal having a low dislocation density and a large area in a short time compared with conventional crystals.

A mixed melt 25 containing sodium and gallium which are raw materials is poured into a reaction chamber 12. An end of a member 26 having wettability to the mixed melt 25 is immersed in the mixed melt 25. A seed crystal 27 of gallium nitride is placed on the surface or in the vicinity of the surface of the member 26. The exposed surface of the member 26 is covered with the thin liquid film of the mixed melt 25 by a wetting phenomenon in a gallium nitride crystal-growing atmosphere. Thus, nitrogen in a gas phase is efficiently dissolved in the liquid film and then the necessary and sufficient concentration of nitrogen for growing the crystal is obtained. Further, the nitride crystal having the low dislocation density and the large area is produced by a flux method in a short time compared with conventional crystals as the mixed melt 25 reaches on the crystal growing surface of the seed crystal 27 by the wetting phenomenon and then the raw materials necessary for crystal growing are sufficiently supplied on the crystal growing surface.