An overtaking assistant system for notifying a driver whether or not a host vehicle is allowed to overtake a first vehicle traveling along a slow lane before the host vehicle when the host vehicle travels along the slow lane, the overtaking assistant system comprising: a speed detector configured to detect a speed of the host vehicle; a preceding vehicle detector configured to detect relative distances and relative speeds of the first vehicle and a second vehicle, the second vehicle traveling along a passing lane before the host vehicle with respect to the host vehicle; a speed comparison unit configured to compare speeds of the first and second vehicles (51,52); an overtaking decision making unit configured to determine whether or not the host vehicle is allowed to overtake the first vehicle; and a notification unit configured to notify a driver of the host vehicle that the host vehicle is allowed to overtake the first vehicle when the overtaking decision making unit determines that the host vehicle is allowed to overtake the first vehicle, characterized in that the preceding vehicle detector has a forward looking camera configured to capture a forward image and to recognize a type of the first vehicle from the captured image, wherein the overtaking decision making unit is configured to determine that the host vehicle is allowed to overtake the first vehicle if the speed of the host vehicle is higher than the speed of the first vehicle and the speed of the second vehicle is higher than the speed of the first vehicle, and on the basis of an entire length of the first vehicle, the relative distance between the host vehicle and the first vehicle, and a safety distance from the first vehicle necessary to be obtained when the host vehicle returns from the passing lane to a slow lane after overtaking the first vehicle, wherein the entire length of the first vehicle is a value preset depending on the type of the first vehicle. a speed detector configured to detect a speed of the host vehicle; a preceding vehicle detector configured to detect relative distances and relative speeds of the first vehicle and a second vehicle, the second vehicle traveling along a passing lane before the host vehicle with respect to the host vehicle; a speed comparison unit configured to compare speeds of the first and second vehicles (51,52); an overtaking decision making unit configured to determine whether or not the host vehicle is allowed to overtake the first vehicle; and a notification unit configured to notify a driver of the host vehicle that the host vehicle is allowed to overtake the first vehicle when the overtaking decision making unit determines that the host vehicle is allowed to overtake the first vehicle, characterized in that the preceding vehicle detector has a forward looking camera configured to capture a forward image and to recognize a type of the first vehicle from the captured image, wherein the overtaking decision making unit is configured to determine that the host vehicle is allowed to overtake the first vehicle if the speed of the host vehicle is higher than the speed of the first vehicle and the speed of the second vehicle is higher than the speed of the first vehicle, and on the basis of an entire length of the first vehicle, the relative distance between the host vehicle and the first vehicle, and a safety distance from the first vehicle necessary to be obtained when the host vehicle returns from the passing lane to a slow lane after overtaking the first vehicle, wherein the entire length of the first vehicle is a value preset depending on the type of the first vehicle.