Lane departure warning apparatus and system

There is provided a lane departure warning apparatus 100 capable of preventing false warnings and absence of a warning regarding lane departure which is attributed to special road geometries such as junctions and tollgates. The lane departure warning apparatus 100 for outputting a warning signal upon determining departure of a vehicle from a lane, performing the steps of: when one dividing line in a vehicle width direction of the vehicle is non-detected, estimating a position of the one dividing line based on a position of the other dividing line as a first estimation dividing line; estimating a position of the non-detected one dividing line based on a position of the one dividing line prior to non-detection as a second estimation dividing line; and comparing the first estimation dividing line with the second estimation dividing line to determine lane departure.