An automatic shift apparatus including a transmission; a vehicle speed acquisition unit; a gear speed acquisition unit that acquires a gear speed of the transmission; a unit that sets, based on a vehicle speed, a minimum allowable gear speed at which a rotation speed of an input shaft of the transmission is equal to or lower than a predetermined rotation speed and which has a highest gear ratio among a plurality of gear speeds; and a unit that determines that the gear speed is abnormal if the gear speed has a higher gear ratio than the minimum allowable gear speed due to a change in the gear speed, and not determining that the gear speed is abnormal if the gear speed has a higher gear ratio than the minimum allowable gear speed due to a change in the minimum allowable gear speed that is set.