A diester-based material production unit comprising: a reaction device including a reaction vessel in which an esterification reaction of dicarboxylic acid and a primary alcohol is performed and a gas phase discharge line installed at an upper end of the reaction vessel such that vaporized primary alcohol and water are discharged to a column therethrough; the column including a column main body in which the gas-liquid separation of the primary alcohol and the water introduced from the gas phase discharge line is performed, a liquid phase line installed at a lower portion of the column main body such that a liquefied alcohol-rich stream flows into the reaction device, and a gas phase line installed at an upper portion of the column main body and connected to a side portion of a flash drum such that a mixture stream of a gas-phase primary alcohol and water flows out; a heat exchanger installed on the gas phase line of the column and removing heat of the gas phase line; the flash drum including a flash drum main body in which separation of a liquid phase and a gas phase is performed in a mixture stream including the primary alcohol and the water, a flash drum lower line from which the liquid including a liquefied primary alcohol is discharged, and a flash drum upper line installed to discharge the mixture stream of the gas-phase primary alcohol and the water to a layer separator; a condenser installed on the flash drum upper line to liquefy the mixture stream of the gas-phase primary alcohol and the water in the flash drum upper line; and the layer separator including a separation tank in which the layer separation of a mixture of the liquefied primary alcohol and the water into an organic layer and an aqueous layer is performed, an organic layer line through which the separated organic layer is discharged, and an aqueous layer line through which the separated aqueous layer is discharged, wherein: the flash drum lower line is connected to one or more positions selected from the group consisting of a column main body side upper portion, a column main body side lower portion, and the reaction vessel; the organic layer line is connected to one or more positions selected from the group consisting of a flash drum main body side portion, the column main body side upper portion, the column main body side lower portion and the reaction vessel; and at least one of the flash drum lower line and the organic layer line is connected to the column main body side upper portion. a reaction device including a reaction vessel in which an esterification reaction of dicarboxylic acid and a primary alcohol is performed and a gas phase discharge line installed at an upper end of the reaction vessel such that vaporized primary alcohol and water are discharged to a column therethrough; the column including a column main body in which the gas-liquid separation of the primary alcohol and the water introduced from the gas phase discharge line is performed, a liquid phase line installed at a lower portion of the column main body such that a liquefied alcohol-rich stream flows into the reaction device, and a gas phase line installed at an upper portion of the column main body and connected to a side portion of a flash drum such that a mixture stream of a gas-phase primary alcohol and water flows out; a heat exchanger installed on the gas phase line of the column and removing heat of the gas phase line; the flash drum including a flash drum main body in which separation of a liquid phase and a gas phase is performed in a mixture stream including the primary alcohol and the water, a flash drum lower line from which the liquid including a liquefied primary alcohol is discharged, and a flash drum upper line installed to discharge the mixture stream of the gas-phase primary alcohol and the water to a layer separator; a condenser installed on the flash drum upper line to liquefy the mixture stream of the gas-phase primary alcohol and the water in the flash drum upper line; and the layer separator including a separation tank in which the layer separation of a mixture of the liquefied primary alcohol and the water into an organic layer and an aqueous layer is performed, an organic layer line through which the separated organic layer is discharged, and an aqueous layer line through which the separated aqueous layer is discharged, wherein: the flash drum lower line is connected to one or more positions selected from the group consisting of a column main body side upper portion, a column main body side lower portion, and the reaction vessel; the organic layer line is connected to one or more positions selected from the group consisting of a flash drum main body side portion, the column main body side upper portion, the column main body side lower portion and the reaction vessel; and at least one of the flash drum lower line and the organic layer line is connected to the column main body side upper portion. the flash drum lower line is connected to one or more positions selected from the group consisting of a column main body side upper portion, a column main body side lower portion, and the reaction vessel; the organic layer line is connected to one or more positions selected from the group consisting of a flash drum main body side portion, the column main body side upper portion, the column main body side lower portion and the reaction vessel; and at least one of the flash drum lower line and the organic layer line is connected to the column main body side upper portion.