An apparatus includes an autoclave for preparing a supercritical solvent, a convection controller for establishing a convection flow, a dissolution zone where a feedstock is located above the convection controller and a crystallization zone where a seed is located below the convection controller are formed. A convection flow rate of the supercritical solution between the dissolution zone and the crystallization zone is determined by the degree of opening of the convection controller and the temperature difference between the dissolution zone and the crystallization zone. Accordingly, the supercritical solution, in which the nitride has a negative temperature coefficient of solubility, is supplied from the dissolution zone to the crystallization zone in which a seed is located through the convection controller so that nitride crystal is selectively grown on the seed by maintaining supersaturation of the supercritical solution with respect to the seed at a raised temperature.