A method for producing a carbonaceous material for a negative electrode of a non-aqueous electrolyte secondary battery, the method comprising: a heat treatment step and a gas treatment step, the heat treatment step comprising: continuously feeding a carbon precursor containing an alkali metal element and/or an alkali metal compound from a feeding unit of a rotary kiln including the feeding unit, a discharge unit, a furnace reactor tube, and an exhaust unit provided inside the furnace reactor tube; introducing a non-oxidizing gas from a gas injection unit provided on the discharge unit side in a direction from the discharge unit side to the feeding unit side; heating the carbon precursor in a temperature range of 1000°C to 1500°C in a non-oxidizing gas atmosphere to produce a carbonaceous material; and discharging the carbonaceous material continuously from the discharge unit, the discharging including suctioning, into the exhaust unit, a non-oxidizing exhaust gas that contains evolved gas containing alkali metal vaporized by the heating and contains a flying carbonaceous matter flying from the carbon precursor and the carbonaceous material; the gas treatment step comprising: blowing the exhaust gas into a cooling can filled with water or an aqueous solution to bring the exhaust gas into direct contact with the water or aqueous solution so that an evolved gas in the exhaust gas is cooled and absorbed, and at the same time, the flying carbonaceous matter is collected in the water or aqueous solution. a heat treatment step and a gas treatment step, the heat treatment step comprising: continuously feeding a carbon precursor containing an alkali metal element and/or an alkali metal compound from a feeding unit of a rotary kiln including the feeding unit, a discharge unit, a furnace reactor tube, and an exhaust unit provided inside the furnace reactor tube; introducing a non-oxidizing gas from a gas injection unit provided on the discharge unit side in a direction from the discharge unit side to the feeding unit side; heating the carbon precursor in a temperature range of 1000°C to 1500°C in a non-oxidizing gas atmosphere to produce a carbonaceous material; and discharging the carbonaceous material continuously from the discharge unit, the discharging including suctioning, into the exhaust unit, a non-oxidizing exhaust gas that contains evolved gas containing alkali metal vaporized by the heating and contains a flying carbonaceous matter flying from the carbon precursor and the carbonaceous material; the gas treatment step comprising: blowing the exhaust gas into a cooling can filled with water or an aqueous solution to bring the exhaust gas into direct contact with the water or aqueous solution so that an evolved gas in the exhaust gas is cooled and absorbed, and at the same time, the flying carbonaceous matter is collected in the water or aqueous solution. continuously feeding a carbon precursor containing an alkali metal element and/or an alkali metal compound from a feeding unit of a rotary kiln including the feeding unit, a discharge unit, a furnace reactor tube, and an exhaust unit provided inside the furnace reactor tube; introducing a non-oxidizing gas from a gas injection unit provided on the discharge unit side in a direction from the discharge unit side to the feeding unit side; heating the carbon precursor in a temperature range of 1000°C to 1500°C in a non-oxidizing gas atmosphere to produce a carbonaceous material; and discharging the carbonaceous material continuously from the discharge unit, the discharging including suctioning, into the exhaust unit, a non-oxidizing exhaust gas that contains evolved gas containing alkali metal vaporized by the heating and contains a flying carbonaceous matter flying from the carbon precursor and the carbonaceous material; the gas treatment step comprising: blowing the exhaust gas into a cooling can filled with water or an aqueous solution to bring the exhaust gas into direct contact with the water or aqueous solution so that an evolved gas in the exhaust gas is cooled and absorbed, and at the same time, the flying carbonaceous matter is collected in the water or aqueous solution.