A bicycle structure comprising: a chain a crankset including a plurality of chain rings, with a largest chain ring of the plurality of chain rings having a plurality of teeth with teeth bottoms interposed between adjacent ones of the teeth; and a front derailleur including a chain guide having a chain guide slot defined by a first chain engagement surface and a second chain engagement surface, wherein the first chain engagement surface is configured to contact an inside surface of a chain to perform an upshifting operation and the second engagement surface is configured to contact an outside surface of the chain to perform a downshifting operation, the first chain engagement surface being provided with a first contact area for engaging the chain during a usual chain shifting operation that moves the chain onto the largest chain ring and a second contact area for contacting the chain during an unusual chain shifting operation that moves the chain onto the largest chain ring, wherein the second contact area has a protruding part that protrudes outwardly from the first chain engagement surface into the chain guide slot, the protruding part being disposed at a front edge of the chain guide that forms a chain exit of the chain guide slot, wherein the protruding part has a radial inner edge with a forward point, wherein, at the forward point of the inner edge, the protruding part being located away from the teeth bottoms of the largest chain ring in a radial outside direction of the largest chain ring, the protruding part being located away from the teeth bottom of the largest chain ring at the forward point in the radial outside direction of the largest chain ring by a prescribed distance as measured along a radius (Rl), the radius extending from the rotational axis of the crankset through the forward point of the inner edge, said prescribed distance being in a range from 90% to 190% of a maximum chain height of the chain. a chain a crankset including a plurality of chain rings, with a largest chain ring of the plurality of chain rings having a plurality of teeth with teeth bottoms interposed between adjacent ones of the teeth; and a front derailleur including a chain guide having a chain guide slot defined by a first chain engagement surface and a second chain engagement surface, wherein the first chain engagement surface is configured to contact an inside surface of a chain to perform an upshifting operation and the second engagement surface is configured to contact an outside surface of the chain to perform a downshifting operation, the first chain engagement surface being provided with a first contact area for engaging the chain during a usual chain shifting operation that moves the chain onto the largest chain ring and a second contact area for contacting the chain during an unusual chain shifting operation that moves the chain onto the largest chain ring, wherein the second contact area has a protruding part that protrudes outwardly from the first chain engagement surface into the chain guide slot, the protruding part being disposed at a front edge of the chain guide that forms a chain exit of the chain guide slot, wherein the protruding part has a radial inner edge with a forward point, wherein, at the forward point of the inner edge, the protruding part being located away from the teeth bottoms of the largest chain ring in a radial outside direction of the largest chain ring, the protruding part being located away from the teeth bottom of the largest chain ring at the forward point in the radial outside direction of the largest chain ring by a prescribed distance as measured along a radius (Rl), the radius extending from the rotational axis of the crankset through the forward point of the inner edge, said prescribed distance being in a range from 90% to 190% of a maximum chain height of the chain.