A transmission mechanism includes a chain. The chain includes a plurality of inner link units and a plurality of outer link units. Each of the inner link units includes two inner chain plates. Each of the inner chain plates has an inner waist section. At least one of the outer link units includes two outer chain plates. Each of the outer chain plates has an outer waist section that has a protruding part and a recessed part. A distance between the inner waist sections of each of the inner link units is smaller than a distance between the protruding parts of the outer chain plates of the at least one of the outer link units, and is equal to or smaller than a distance between the recessed parts of the at least one of the outer link units.