If the difference of the manual driving operation amount, detected by a manual driving operation amount detection portion, from the autonomous driving operation amount, calculated by an autonomous driving operation amount calculation portion, is equal to or smaller than an operation amount threshold during manual driving, a driving state switching portion switches the driving state from manual driving to autonomous driving in response to an autonomous driving switching request from a host vehicle's driver. This configuration prevents the switching from manual driving to autonomous driving if the driver's manual driving operation differs much from the autonomous driving operation with a high possibility that the autonomous driving operation suitable for the actual traveling environment will not be performed. Therefore, this configuration prevents the switching from manual driving to autonomous driving if the possibility is high that the autonomous driving operation suitable for the actual traveling environment will not be performed.