An apparatus for producing powders of metal compound containing oxygen comprising a liquid flow controller, a vaporizer and a reactor, which consists essentially of: means for feeding a gas containing a material and oxygen; means for heating the gas from the side surface of the feeding means; means for cooling the gas positioned at the downstream side of the feeding means; and means for receiving the product generated by the reaction. A process and products for producing powders of metal compound containing oxygen comprising the steps of: feeding at least one material selected from a liquid material and a solution material obtained by dissolving solid ingredient in organic solvent via a liquid flow controller into a vaporizer; vaporizing the materials in the vaporizer; adding oxygen; heating; cooling; and crystallizing. The process and the apparatus enable easily mass-producing fine powders of metal compound containing oxygen used as materials for optical crystals, nonlinear crystals or magneto-optical crystals with reasonable production cost.