PURPOSE: To effectively prevent a high temperature part from being locally generated and to effect a stable vapor-phase cracking of carbon tetrachloride with high efficiency by setting a value obtained by dividing the ratio of the axial length of a catalyst to the diameter of the catalyst layer by a heat removing rate to a specific value or more.

CONSTITUTION: Assuming that a ratio (L/O)/η, is 3 or more, a reaction is carried out. Herein, L is the axial length of a catalyst layer and D is the diameter of the catalyst layer. The η is heat removing rate expressed by Q2/Q1=1. The Q1 is a heating value produced by the reaction and the Q2 is the removing quantity of heat exhausted out of a system. Thus, the reactivity of carbon tetrachloride can be set to about 98%.