NOVELTY - Extracting essential oil from biomass wastes comprises: (a) heating up indirectly biomass raw wastes in an air-tight reaction vessel (1) to produce a thermal pyrolysis cracking reaction; (b) guiding smoky gas which is distilled from executing the thermal pyrolysis cracking to the raw materials into a condenser (2) to condense as liquid; (c) guiding the condensate into a separation tank (3) to separate into water and oil; and (d) discharging outside non-liquefied gas which has been undergone with the condensation and separation steps, by a suction pump (4).    USE - The process is useful for extracting essential oil from biomass wastes (claimed) such as wood wastes, wood chips or other plants.    ADVANTAGE - In the process, air is sucked out in a short time by a high-speed suction pump depending upon internal pressure and distilled substance in the reaction vessel, so as to maintain a low pressure and prevent the distilled substance from staying in the reaction vessel for too long time that the distilled substance is scorched excessively, hence the processing time can be shortened, essential oil of high quality and high yield and activated carbons as by-products can be acquired.    DETAILED DESCRIPTION - Extracting essential oil from biomass wastes comprises: (a) heating up indirectly biomass raw wastes in an air-tight reaction vessel (1), an interior of which is kept at low vacuum and is oxygen-free, to produce a thermal pyrolysis cracking (i.e. dry distillation) reaction; (b) guiding smoky gas which is distilled from executing the thermal pyrolysis cracking to the raw materials into a condenser (2) to condense as liquid; (c) guiding the condensate into a separation tank (3) to separate into water and oil; and (d) discharging outside non-liquefied gas which has been undergone with the condensation and separation steps, by a suction pump (4), where during implementing the above steps, temperature and pressure of the reaction vessel are divided into at least two phases for control which includes automatically or manually controlling the suction pump to execute short and high-speed suction in a large amount timely, so as to allow the thermally disintegrated gas not to remain in the reaction vessel for too long time that ingredient is reconstituted, and to keep at all time internal pressure of the reaction vessel at a pre-determined low pressure condition. An INDEPENDENT CLAIM is included for a device for extracting essential oil from biomass wastes, comprising a reaction vessel having an external vessel, an outer peripheral wall of which is provided with an electrothermal device and a thermal insulation humectant, and an inner vessel which is removably emplaced in the external vessel to hold raw materials; a condenser which is provided at a downstream side of the reaction vessel to condense gas distilled from the reaction vessel; a separation tank which is provided at a downstream side of the condenser to separate liquid condensed from the condenser into water and oil; a suction pump which is provided at a downstream side of the separation tank to discharge non-condensed and non-liquefied gas out of the system; and a control booth (5) which is used to adjust and control temperature and pressure in the reaction vessel and is connected to the suction pump.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of components of a system which extracts essential oil from biomass wastes.    Reaction vessel (1)    Condenser (2)    Separation tank (3)    Suction pump (4)    Control booth. (5)