An apparatus for implementing a lane change decision aid system (LCDAS) includes: a sensing unit sensing whether there is a target vehicle in adjacent zones, a rear zone, or a forward zone of a subject vehicle; a determination unit determining an activation condition for determining whether an LCDAS function is active/inactive and a warning condition for determining whether a warning of the LCDAS function is issued/un-issued, based on the sensing of the sensing unit; a warning unit issuing the warning to a driver based on the determination of the determination unit; and a control unit controlling the sensing unit, the determination unit, and the warning unit.