A driving assist system for assisting manual effort by an operator to operate an accelerator pedal of a motor vehicle, the driving assist system comprises a data acquisition sub-system acquiring data including information on state of the motor vehicle and information on environment in a field around the motor vehicle. Control logic determines the degree of risk in the field around the motor vehicle in response to the acquired data. An actuator is provided, which is operable in response to a command for generating reaction force at the accelerator pedal. Control logic simply increases an increment of reaction force between a first reaction force increment and a second reaction force increment as the determined degree of risk grows from a predetermined cutoff value to a predetermined critical value to determine the command for regulating the actuator to realize the increment in reaction force. The first reaction force increment has a first magnitude in an area of a lower limit of a predetermined range, in magnitude, of increment in reaction force, which the vehicle operator can perceive through the sense of touch during depressing the accelerator pedal. The second reaction force increment has a second magnitude in an area of an upper limit of the predetermined range.