A vehicle speed limiting system having a throttle-by-wire mechanism that drives a throttle valve using a motor, the vehicle speed limiting system comprising: a three-dimensional map that is provided to each of gear stages of a transmission and from which to derive a target throttle valve opening degree (θB) of the throttle valve on a basis of a throttle grip opening degree (θA) and an engine speed; a throttle valve driving unit that drives the motor in accordance with the target throttle valve opening degree, wherein, when a speed of a vehicle is about to exceed a preset maximum speed, the throttle valve driving unit drives the motor in such a manner that the speed of the vehicle does not exceed the preset maximum speed, irrespective of the target throttle valve opening degree (θB) derived from the three-dimensional map, speed difference calculating means for calculating a difference between a current speed of the vehicle and the preset maximum speed; acceleration calculating means for calculating an acceleration of the vehicle; and maximum speed limiter opening degree calculating means for calculating a first maximum speed limiter opening degree by adding a first predetermined opening degree, a second predetermined opening degree, and a current throttle valve opening degree, the first predetermined opening degree being calculated by multiplying the speed difference by a preset P-term coefficient, the second predetermined opening degree being calculated by multiplying the acceleration by a preset D-term coefficient, wherein the throttle valve driving unit is configured to drive the motor on a basis of the first maximum speed limiter opening degree once the calculated first maximum speed limiter opening degree falls below the target throttle valve opening degree (θB) derived on a basis of the three-dimensional map. a three-dimensional map that is provided to each of gear stages of a transmission and from which to derive a target throttle valve opening degree (θB) of the throttle valve on a basis of a throttle grip opening degree (θA) and an engine speed; a throttle valve driving unit that drives the motor in accordance with the target throttle valve opening degree, wherein, when a speed of a vehicle is about to exceed a preset maximum speed, the throttle valve driving unit drives the motor in such a manner that the speed of the vehicle does not exceed the preset maximum speed, irrespective of the target throttle valve opening degree (θB) derived from the three-dimensional map, speed difference calculating means for calculating a difference between a current speed of the vehicle and the preset maximum speed; acceleration calculating means for calculating an acceleration of the vehicle; and maximum speed limiter opening degree calculating means for calculating a first maximum speed limiter opening degree by adding a first predetermined opening degree, a second predetermined opening degree, and a current throttle valve opening degree, the first predetermined opening degree being calculated by multiplying the speed difference by a preset P-term coefficient, the second predetermined opening degree being calculated by multiplying the acceleration by a preset D-term coefficient, wherein the throttle valve driving unit is configured to drive the motor on a basis of the first maximum speed limiter opening degree once the calculated first maximum speed limiter opening degree falls below the target throttle valve opening degree (θB) derived on a basis of the three-dimensional map.