Evaporative fuel processing system for in-cylinder fuel injection type internal combustion engine and method

An evaporative fuel processing system for an in-cylinder injection type internal combustion engine (10) includes an evaporative fuel processing mechanism (90) that includes a canister (91) to which an evaporative fuel in a fuel supply system is adsorbed and performs an operation for purging the adsorbed evaporative fuel into an intake system of the internal combustion engine. The system further includes a controller (50) that estimates a degree of dilution occurred in a lubricating oil for the internal combustion engine with a fuel mixed therewith, and inhibits the purging operation performed by the evaporative fuel processing mechanism (90) when the estimated degree of dilution is equal to or larger than a predetermined value.