In a speed-change operation mechanism, a main body of a lock member is disposed to produce a clearance between the main body and the surface of the handle arm, whereas a pivot operation part of the lock member is disposed to close a clearance between the main body and the surface of the handle arm and simultaneously to produce a clearance between the pivot operation part and the surface of the handle arm. A relatively large clearance is produced between the main body of the lock member and the surface of the handle arm, whereas a small clearance, just enough to allow a pivot operation of the lock member, is produced between the pivot operation part of the lock member and the surface of the handle arm.
