A travel assist system searches a nearest service station based on navigation information and predicts a quantity of aqueous urea solution consumed until the service station is reached. If a quantity of the remaining aqueous urea solution is not greater than the aqueous urea solution consumption at least by a predetermined value, a warning is provided to a user. Control conditions of an internal combustion engine (diesel engine) enabling the vehicle to reach the service station without running short of the aqueous urea solution are calculated. An exhaust gas recirculation quantity is increased based on the calculation result. Thus, nitrogen oxides contained in the exhaust gas is reduced and a consumption of the aqueous urea solution is reduced.