PURPOSE: To optimally control the energization of an electric heater in accordance with a composition of gasoline in an internal combustion engine in which reformed gasoline and normal gasoline are alternatively fed into an engine or the mixture thereof is fed into the engine, and which incorporates a catalyst device incorporating an electric heater, for purifying exhaust gas.

CONSTITUTION: A power feed setting means F sets a power to be fed in accordance with a composition of gasoline detected by a fuel composition detecting means E, and the set power is then fed to an electric heater D in a catalyst device C.