In a chain guide mechanism having a guide bridge for integrally holding two chain guides, a chain and a driving sprocket for more efficient assembly and maintenance, the guide bridge has a oil inlet on a surface of its sprocket-pressing base for receiving oil from an oil supply port in an engine block on which the guide bridge is mounted. The oil inlet communicates, through an internal passage within the base of the guide bridge, with an oil discharge port within a groove in which teeth of the driving sprocket travel.