Drive system changing device and method/program thereof

A drive system changing device actuated in an emergency operation is characterized by having a vehicle speed detecting means (5) for detecting a vehicle speed before a deceleration; a deceleration detecting means (6) for detecting a negative acceleration due to a sudden braking; a steering angle detecting means (7) for detecting a steering angle when a sudden operation is performed in the sudden braking; a determination means (3) for determining whether or not to change a drive system from a result obtained from each of the above detecting means (5,6,7); a driving force separating means (2) for changing a four wheel drive system to front/rear wheel drive systems by separating a part of driving force transmitting unit of the four wheel drive system according to a determination of the determination means (3); and a drive system returning means (2) for returning the drive system changed to the front/rear wheel drive systems after the emergency operation by the separating means to the four wheel drive system.