A contra-rotating mechanism includes master and slave shafts coaxially arranged to rotate in first and second directions, the first direction being opposite to the second, a master driving member fixed around and to the master shaft to rotate therewith; a plurality of drive-transfer units symmetrically and radially arranged around the master driving member and receiving a driving force from the master to rotate in the second direction; a plurality of rotation reversing units symmetrically and radially arranged around the slave shaft, each rotation-reversing unit disposed between corresponding neighboring drive-transfer units of the drive-transfer units and configured to receive rotation-force from the corresponding drive-transfer units to rotate in the first direction, a slave driven member fixed around the slave shaft to rotate therewith in the second direction, the slave driven member to mesh with the plurality of rotation-reversing units to rotate in the second direction; and first and second panels.