A blow-by gas refluxing device is provided for an engine system including an engine and an intake air passage communicating with the engine for supplying intake air into the engine. The blow-by gas refluxing device includes a plurality of blow-by gas refluxing passages each having an inlet communicating with the engine and an outlet communicating with the intake air passage. The outlets of the blow-by gas passages communicate with the intake air passage at different positions along the length of the intake air passage and each of the blow-by gas passages has a backflow preventing device disposed therein, so that blow-by gas produced in the engine can flow into the intake air passage via at least one of the blow-by gas refluxing passages throughout the entire operational range of the engine.