An apparatus for manufacturing a group III nitride single crystal including: a reaction vessel including a reaction area, wherein in the reaction area, a group III source gas and a nitrogen source gas are reacted such that a group III nitride crystal is grown on a substrate; a susceptor arranged in the reaction area and supporting the substrate; a group III source gas supply nozzle supplying the group III source gas to the reaction area; and a nitrogen source gas supply nozzle supplying the nitrogen source gas to the reaction area, wherein the nitrogen source gas supply nozzle is configured to supply the nitrogen source gas and at least one halogen-based gas selected from the group consisting of a hydrogen halide gas and a halogen gas to the reaction area.