NOVELTY - The raw material organic substance (1) having organic group waste material is thermally reacted at 1100degreesC or less, and converted into gas (2) and char (4). The gas is directly contacted with tar liquid (3), and gaseous tar contained in gas is condense-liquefied and transferred to tar liquid from gas. The tar liquid maintained at high temperature is gasified with raw material, and gasification efficiency of raw material organic substance is improved.    USE - For gasifying organic waste material, such as biomass, industrial waste such as construction waste, animal and plant residue, sludge, paper, plastic and organic refuse, and producing fuel gas.    ADVANTAGE - The organic substance such as waste material is effectively used for production of fuel gas. The gasification efficiency is improved by recycling the separated tar to decomposition apparatus. The corrosion of metal material of rotary kiln is prevented.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for gasifier of organic substance. The gasifier has thermochemical converter (A1) for carrying out thermal reaction at 1100degreesC or less, and tar separation apparatus (B) for directly contacting tar liquid and gas produced by thermal reaction of waste material. The gaseous tar contained in gas is transferred to tar liquid. The tar liquid is cooled and circulated to apparatus (B). An increased portion of tar liquid is fed to thermochemical converter, and gasified. The converter (A1) carries out thermal reaction optionally in the presence of gasifying agent, such as water vapor, carbon dioxide and combustion gas.    DESCRIPTION OF DRAWING(S) - The figure shows the block diagram of gasifier.    raw material (1)    thermal decomposition gas (2)    tar (3)    char (4)    source gas (5)    clean gas (6)    combustion gas (7)    super heated steam (8)    gasifying agent (9)    vapor (10)    gas electric power generation waste gas (11)    thermochemical converter (A1)    tar separation apparatus (B)    gas purification apparatus (C)