To provide a catalyst heat deterioration suppression device that prevents heat deterioration of a catalytic converter by reducing an oil lift and a backflow of unburnt gas in a crankcase into a combustion chamber due to negative pressure while sufficiently ensuring engine brake force during a deceleration fuel cut.

An internal cylinder pressure regulating means regulates an internal cylinder pressure of an internal combustion engine. During a deceleration fuel cut (S12), the internal cylinder pressure regulating means controls an index (intake manifold pressure) correlated with sealing force of a piston ring fitted on a piston of the internal combustion engine into a given range to regulate the internal cylinder pressure (S14).