In an adaptive cruise control (ACC) region where vehicle speed V is greater than a predetermined third vehicle speed #V3, a decrease amount of a target inter-vehicle distance per predetermined unit vehicle speed decrease amount in a state where the vehicle speed V is less than a predetermined fourth vehicle speed #V4 is smaller than a decrease amount of the target inter-vehicle distance per predetermined unit vehicle speed decrease amount in a state where the vehicle speed V is greater than the predetermined fourth vehicle speed #V4. The decrease amount of the target inter-vehicle distance per predetermined unit vehicle speed decrease amount in a state where the vehicle speed V is less than a predetermined first vehicle speed #V1 is larger than a decrease amount of the target inter-vehicle distance per predetermined unit vehicle speed decrease amount in a state where the vehicle speed V is greater than the predetermined first vehicle speed #V1 and less than a predetermined second vehicle speed #V2.