A gear change control system of an automatic transmission, includes: a shift member, including a shaft portion disposed in such a manner that a selection axis is oriented in a selecting direction, and including a pair of arm portions formed on the shaft portion in such a manner as to project therefrom; shift rail members, having rail shaft portions, and arranged in such a manner that shift axes are oriented in a shifting direction; shift fork portions, formed on the rail shaft portions; shift lug members, formed on the rail shaft portions and including pillar-shaped portions. The pair of the arm portions swing about the selection axis to apply a pressure in the shifting direction from one side of the pillar-shaped portion by one of the arm portions so as to cause the shift fork portion to perform a shift making operation, and to apply a pressure in the shifting direction from the other side of the pillar-shaped portion by the other arm portion so as to cause the shift fork portion to perform a shift withdrawing operation.