PURPOSE: To carry out a gear change control matched with each traveling condition by automatically switching over the gear change pattern of an automatic transmission being interlocked with the switchover between 2-wheel driving and 4-wheel driving.

CONSTITUTION: A sub-transmission 4 is connected to front and rear wheels via a 2-4 switchover mechanism 5, and a switchover control between 2-wheel driving and 4-wheel driving is carried out by means of a switchover motor 15. At the time of switching between 2-wheel and 4-wheel driving, a gear change pattern switchover means 17a carries out the automatic switchover of the gear change patterns for 2-, 4-wheel driving based on a signal from a 2-4 switchover means 16. Thereby, a gear change control matched with each traveling condition can be smoothly carried out.