A chain guide for guiding a chain includes a chain passage formed by an outer side wall and an inner side wall for surrounding the chain passage. A front end portion of the inner side wall is retracted to and is positioned at a rear side of a vehicle body than a front end portion of the outer side wall. Guide ribs are formed on an upper wall and a bottom wall and are brought into sliding contact with upper and lower sides of the chain. A discharge recessed portion which is opened frontwardly from the front end portion is formed in the inner side wall, wherein the chain passage is in communication with the outside through the discharge recessed portion. Mud or the like which is carried into an inlet falls in the inside of a vehicle body disposed outside the chain guide from the discharge recessed portion