To immediately start braking operation when situation that requires rapid braking is generated, to reduce difference in driving operation from usual traveling and to perform constant speed traveling control capable of reducing a sense of incongruity of the driver.

The device is constituted such that acceleration pedal operation is continuously performed by the driver even after the constant speed traveling control is started. Thereby, even if the situation requiring rapid braking is generated, the braking operation can be immediately started. After starting of the constant speed traveling control, an operation amount of the acceleration pedal corresponding to a target vehicle speed is memorized and when it is detected that the acceleration pedal operation exceeding dead zone is performed relative to the memorized operation amount, the target vehicle speed is changed. As a result, the difference in driving operation from usual traveling can be reduced and the sense of incongruity of the driver can also be reduced.