An automotive arithmetic system mounted on a motor vehicle, the automotive arithmetic system comprising: a main arithmetic device including a first route generation unit that estimates a vehicle external environment including a road and an obstacle using deep learning based on an output from an information acquisition device that acquires information of the vehicle external environment, and generates a first route on the road for avoiding the obstacle based on the estimated vehicle external environment, and a second route generation unit that recognizes the vehicle external environment based on the output from the information acquisition device according to a rule base based on a predetermined rule without using deep learning, specifies a safe area (SA1, SA2) on the road for avoiding the obstacle based on the recognized vehicle external environment, and sets a second route that runs in the safe area (SA1, SA2), the main arithmetic device determining a target motion of the motor vehicle so that the motor vehicle travel on the first route and outputting a control signal for achieving the target motion to actuators that respectively generate a driving force, a braking force, and a steering angle; and a backup arithmetic device including a stop route generation unit that generates a third route, which is a travel route that the traveling motor vehicle takes until the motor vehicle stops at a stop position that satisfies a preset criterion, based on the output from the information acquisition device, the backup arithmetic device determining a backup target motion for causing the motor vehicle to travel on the third route and outputting a backup control signal for achieving the backup target motion to the actuators, wherein the first route generation unit sets the first route in consideration of the safe area (SA1, SA2) set by the second route generation unit, and the automotive arithmetic system outputs the backup control signal to the actuators in preference to the control signal when the main arithmetic device fails. a main arithmetic device including a first route generation unit that estimates a vehicle external environment including a road and an obstacle using deep learning based on an output from an information acquisition device that acquires information of the vehicle external environment, and generates a first route on the road for avoiding the obstacle based on the estimated vehicle external environment, and a second route generation unit that recognizes the vehicle external environment based on the output from the information acquisition device according to a rule base based on a predetermined rule without using deep learning, specifies a safe area (SA1, SA2) on the road for avoiding the obstacle based on the recognized vehicle external environment, and sets a second route that runs in the safe area (SA1, SA2), the main arithmetic device determining a target motion of the motor vehicle so that the motor vehicle travel on the first route and outputting a control signal for achieving the target motion to actuators that respectively generate a driving force, a braking force, and a steering angle; and a first route generation unit that estimates a vehicle external environment including a road and an obstacle using deep learning based on an output from an information acquisition device that acquires information of the vehicle external environment, and generates a first route on the road for avoiding the obstacle based on the estimated vehicle external environment, and a second route generation unit that recognizes the vehicle external environment based on the output from the information acquisition device according to a rule base based on a predetermined rule without using deep learning, specifies a safe area (SA1, SA2) on the road for avoiding the obstacle based on the recognized vehicle external environment, and sets a second route that runs in the safe area (SA1, SA2), the main arithmetic device determining a target motion of the motor vehicle so that the motor vehicle travel on the first route and outputting a control signal for achieving the target motion to actuators that respectively generate a driving force, a braking force, and a steering angle; and a backup arithmetic device including a stop route generation unit that generates a third route, which is a travel route that the traveling motor vehicle takes until the motor vehicle stops at a stop position that satisfies a preset criterion, based on the output from the information acquisition device, the backup arithmetic device determining a backup target motion for causing the motor vehicle to travel on the third route and outputting a backup control signal for achieving the backup target motion to the actuators, wherein the first route generation unit sets the first route in consideration of the safe area (SA1, SA2) set by the second route generation unit, and the automotive arithmetic system outputs the backup control signal to the actuators in preference to the control signal when the main arithmetic device fails.