A simple-structured, easy-to-produce chain drive mechanism is provided, which can reduce the overall noise level irrespective of chain length or rpm, while suppressing noise and vibration caused by tension fluctuations and maintaining durability and service life. The engagement/seating mode between a silent chain and a driving sprocket is one of inside-flank engagement/inside-flank seating, inside-flank engagement/outside-flank seating, outside-flank engagement/inside-flank seating, and outside-flank engagement/outside-flank seating. The engagement/seating mode between the silent chain and a driven sprocket is one of inside-flank engagement/inside-flank seating, inside-flank engagement/outside-flank seating, outside-flank engagement/inside-flank seating, and outside-flank engagement/outside-flank seating. The engagement/seating mode between the chain and the driving sprocket is different from that between the chain and the driven sprocket.