PURPOSE: An alcohol reformer in which a path for conducting exhaust gas through a regenerator to the reformer as well as another path for leading directly to the regenerator are formed and their flow area ratio is switched according to the engine operation conditions by a controlling means, thus permitting the stabilized reformation reaction.

CONSTITUTION: The exhaust inlet of the exhaust path 11 connecting to the exhaust manifold of the engine is branched into a path 11A leading to the top of the regenerator 12 and another path 11B. Further, a controlling valve 19 is used to control the flow area ratio of the paths 11A and 11B at the branch. Before the warming up of the engine, the exhaust gas is directly introduced into the reformer without passing through the regenerator 12 and passed through the evaporator 16 to the outlet 25. After the temperature of the catalyst in the reformer 13 has risen, the condition is detected to rotate the valve 19 gradually counterclockwise through the negative pressure actuator 24 by the controller 23 and feed the exhaust gas to the regenerator 12 to eliminate the fluctuation of the temp. of the exhaust gas by means of the regenerator, thus controlling the reforming gas formation reaction by the reformer 13 and giving a gas mainly consisting of hydrogen and carbon monoxide.