A system for producing an organic substance, comprising: a synthesis gas generation furnace for producing a synthesis gas by partially oxidizing a waste comprising a carbon source; a synthesis gas purification unit which is connected to the synthesis gas generation furnace and purifies the synthesis gas generated in the synthesis gas generation furnace to reduce an impurity concentration in the synthesis gas; and an organic substance synthesis unit which is connected to the synthesis gas purification unit and generates an organic substance from the synthesis gas purified in the synthesis gas purification unit, wherein the synthesis gas purification unit comprises: a first purification unit for purifying the synthesis gas; a second purification unit for purifying the synthesis gas purified in the first purification unit; a detection unit for measuring an impurity concentration in the synthesis gas purified in the first purification unit, wherein the first purification unit is a pressure swing adsorption apparatus or a temperature swing adsorption apparatus, and the detection unit is configured to: feed the synthesis gas purified in the first purification unit to a part positioned downstream of the second purification unit while bypassing the second purification unit when the impurity concentration is not higher than a predetermined value, or feed the synthesis gas purified in the first purification unit to the second purification unit when the impurity concentration is higher than the predetermined value. a synthesis gas generation furnace for producing a synthesis gas by partially oxidizing a waste comprising a carbon source; a synthesis gas purification unit which is connected to the synthesis gas generation furnace and purifies the synthesis gas generated in the synthesis gas generation furnace to reduce an impurity concentration in the synthesis gas; and an organic substance synthesis unit which is connected to the synthesis gas purification unit and generates an organic substance from the synthesis gas purified in the synthesis gas purification unit, wherein the synthesis gas purification unit comprises: a first purification unit for purifying the synthesis gas; a second purification unit for purifying the synthesis gas purified in the first purification unit; a detection unit for measuring an impurity concentration in the synthesis gas purified in the first purification unit, a first purification unit for purifying the synthesis gas; a second purification unit for purifying the synthesis gas purified in the first purification unit; a detection unit for measuring an impurity concentration in the synthesis gas purified in the first purification unit, wherein the first purification unit is a pressure swing adsorption apparatus or a temperature swing adsorption apparatus, and the detection unit is configured to: feed the synthesis gas purified in the first purification unit to a part positioned downstream of the second purification unit while bypassing the second purification unit when the impurity concentration is not higher than a predetermined value, or feed the synthesis gas purified in the first purification unit to the second purification unit when the impurity concentration is higher than the predetermined value. feed the synthesis gas purified in the first purification unit to a part positioned downstream of the second purification unit while bypassing the second purification unit when the impurity concentration is not higher than a predetermined value, or feed the synthesis gas purified in the first purification unit to the second purification unit when the impurity concentration is higher than the predetermined value.