In an exhaust system of an internal combustion engine having a plurality of cylinders, a control valve is disposed downstream of a junction point of one of two exhaust passages of the engine, and a control valve and a catalytic converter are disposed downstream of a junction point of the other of the exhaust passages. The control valves of the two exhaust passages are controlled so that exhaust gas of all of the cylinders mainly passages the catalytic converter of the other exhaust passage during startup of the engine.