a first and second converter are connected via an exhaust passage so that the first converter is situated further upstream relative to the flow of exhaust . these converters comprise an adsorbent which adsorbs hydrocarbons at a temperature lower than a first temperature and discharges hydrocarbons at a temperature higher than the first temperature , and a catalyst which oxidizes hydrocarbons when a second temperature higher than the first temperature is exceeded . the heat capacity of the exhaust passage is set so that the temperature of the adsorbent of the second converter does not reach the first temperature before the catalyst of the first converter reaches the second temperature . by repeating this hydrocarbon adsorption / oxidation , the hydrocarbon discharge amount is reduced especially during a cold start of the engine .