PURPOSE: A carbonaceous substance is pyrolyzed by rapidly heating up to a specific temperature in a hydrogen atmosphere containing methane to increase the yield of light fractions including gasoline with reduced gas formation and decreased hydrogen consumption.

CONSTITUTION: In the gasification or liquefaction of carbonaceous substances, the pyrolysis is carried out in a hydrogen atmosphere containing 10W60v% of methane at a pressure of 20W150kg/cm2G, preferably in the presence of at least one selected from compounds of a metal of group VI or VIII in the periodic table by heating rapidly up to 600W850°C. More preferably, rapid heating is first effected at 600W800°C, then pyrolysis is conducted at 650W850°C.