A running control device of a vehicle including an engine and a brake booster amplifying a brake force by forming a negative pressure in a negative pressure tank by rotation of the engine, the running control device of a vehicle being configured to execute an engine brake running mode performed with the engine coupled to wheels such that an engine brake is applied by driven rotation of the engine and an inertia running mode performed with an engine brake force made lower than that of the engine brake running mode, the running control device of a vehicle executing a first inertia running mode performed with the rotation of the engine stopped and a second inertia running mode performed with the engine kept rotating as the inertia running mode in accordance with predefined respective execution conditions, the running control device of a vehicle comprising a prediction portion configured to predict a necessity of the negative pressure, characterized in that the necessity of the negative pressure being included in a condition for starting of each of the first inertia running mode and the second inertia running mode, the first inertia running mode being started on the condition that the necessity of the negative pressure is equal to or less than a predefined first determination value, and the second inertia running mode being started even when the necessity of the negative pressure is higher than the first determination value, wherein either the second inertia running mode is started when the necessity of the negative pressure is in a region exceeding the first determination value (α1, α2, α3) and equal to or less than a second determination value (β1, β2) higher than the first determination value, and the engine brake running mode is executed when the necessity of the negative pressure is larger than the second determination value (β1, β2), or the second inertia running mode is operable to be started when the necessity of the negative pressure is in a region equal to or less than the second determination value (β1, β2) including a region equal to or less than the first determination value (α1, α2, α3), one of the first inertia running mode and the second inertia running mode is selected to start the one of the first inertia running mode and the second inertia running mode in an overlapping region equal to or less than the first determination value (α1, α2, α3), and the engine brake running mode is executed when the necessity of the negative pressure is larger than the second determination value (β1, β2). the second inertia running mode is started when the necessity of the negative pressure is in a region exceeding the first determination value (α1, α2, α3) and equal to or less than a second determination value (β1, β2) higher than the first determination value, and the engine brake running mode is executed when the necessity of the negative pressure is larger than the second determination value (β1, β2), or the second inertia running mode is operable to be started when the necessity of the negative pressure is in a region equal to or less than the second determination value (β1, β2) including a region equal to or less than the first determination value (α1, α2, α3), one of the first inertia running mode and the second inertia running mode is selected to start the one of the first inertia running mode and the second inertia running mode in an overlapping region equal to or less than the first determination value (α1, α2, α3), and the engine brake running mode is executed when the necessity of the negative pressure is larger than the second determination value (β1, β2).