A CPU computes a throttle opening degree increasing speed Vh and a steering wheel angular velocity V based on a throttle opening degree h and a steering wheel angle . Based on the throttle increasing speed Vh and the steering wheel angular velocity V, the CPU selects one of a first drive mode and a second drive mode. The CPU controls the power transmission ratio of a power transmitting device according to the selected drive mode. Therefore, the power transmission ratio of the power transmitting device is properly controlled in accordance with the degree of intention for acceleration of the driver, which is computed based on the throttle increasing speed Vh, and the turning speed of the steering wheel, which is computed based on the steering wheel angular velocity V. Therefore, the drive mode is properly switched in accordance with the driving state of a four-wheel drive vehicle.