Disclosed is a novel method for steam reforming, by which selectivity to carbon monoxide is high, which is free from various side reactions, which may be carried out at a lower temperature and at a lower pressure than the conventional methods, and which may be carried out even if a catalyst is not used. In the method of the present invention, direct current pulse discharge is performed in a mixed gas containing a gaseous chain hydrocarbon and water vapor so as to react the chain hydrocarbon and the water vapor, thereby generating hydrogen and carbon monoxide.
