As a front monitoring system of a vehicle with strict restrictions on device arrangement, in a case where one or a plurality of external sensors are installed, an exit wave emitted from the external sensors and reflected by a structural object inside the vehicle is prevented from reentering the external sensor, and erroneous detection of an object is suppressed. As a front monitoring system therefor, an external sensor that is mounted inside a vehicle, emits an exit wave toward a front of the vehicle, and acquires a reflected wave entering the external sensor as a detection signal, and a removing means that removes the exit wave emitted by the external sensor and incident on a structural object installed inside the vehicle in a specific direction, particularly at an incident angle larger than a predetermined angle are provided.