NOVELTY - A raw material gas (A) is cooled, condensed and subjected to gas-liquid separation. The obtained liquid is supplied to distillation column. Gas obtained after condensing the separated gas, is divided into portions (I,II). Portion (I) is fed to column, and portion (II) is compressed, cooled, condensed and fed to the column as reflux. Heavy fraction containing hydrocarbon is obtained from bottom portion of column.    USE - For separating hydrocarbon from off-gas, such as natural gas and petroleum associated gas emitted from refinery or petrochemical plant.    ADVANTAGE - The novel method separates hydrocarbon efficiently and economically, without reducing energy efficiency.    DETAILED DESCRIPTION - A raw material gas (A) containing methane and low volatile hydrocarbon is cooled, and portion of cooled gas is condensed and subjected to gas-liquid separation. The separated liquid is supplied to a distillation column, and the gas is expanded in an expander. Portion of expanded gas is condensed, and obtained liquid is supplied to column. The separated gas is divided into portions (I,II). Portion (I) is fed to column, and portion (II) is compressed, cooled and condensed. Pressure of the resultant liquid is reduced and fed to the column as reflux. Residual gas (C) and heavy fraction are obtained from the top and bottom portions of column, respectively. Gas (C) contains methane as main component and small amount of hydrocarbon. Heavy fraction comprises hydrocarbon as main component and small amount of methane.    An INDEPENDENT CLAIM is included for a hydrocarbon separation apparatus having distillation column, cooling separation unit, line supplying liquid to distillation column, expander (5), gas-liquid separator (7) connected to the exit of expander, line supplying condensate to column, branched unit for dividing the obtained gas, line supplying portion (I) to column, compression unit, cooling unit, pressure reduction unit and line supplying reflux.    DESCRIPTION OF DRAWING(S) - The figure shows the process flow diagram of the above ethane recovery method. (Drawing includes non-English language text).    raw material gas coolers (1,3)    expander (5)    gas-liquid separator (7)    compressor (8)    reflux condenser (10)    raw material gas (A)    residual gas (C)