Abstract: Disclosed are an apparatus and method for treating organic waste to reduce treatment costs and period, enable environmentally friendly treatment without causing bad smell or waste water, and thereby prepare an organic combust with a high quality and a liquid fertilizer with a high concentration. The apparatus includes a sealable reaction vessel including an inlet through which an organic waste and a reactive additive are injected, an outlet through which a treated substance is discharged as reactive gas, a stirrer to stir contents of the reaction vessel, and a liquid fertilizer producer to condense the reactive gas discharged from the gas outlet with a cooling solution and thereby produce a liquid fertilizer, while gradually increasing the concentration of fertilizer components of the cooling solution.