An exhaust system of an internal combustion engine having at least one
cylinder comprises a main exhaust passage connected to the cylinder; a
main catalytic converter disposed in the main exhaust passage; a bypass
exhaust passage that diverges from the main exhaust passage, the bypass
exhaust passage having a gas flow resistance larger than that of the main
exhaust passage and having a downstream end connected to the main exhaust
passage at a position upstream of the main catalytic converter; an
auxiliary catalytic converter disposed in the bypass exhaust passage; and
a gas flow switching device that is capable of forcing exhaust gas from
the cylinder of the engine to flow toward the bypass exhaust passage when
assuming a given operation position.