A lane change decision aid system apparatus, comprising: a sensing unit sensing whether there is a target vehicle in adjacent zones, a rear zone, or a forward zone of the subject vehicle; a determination unit determining an activation condition of activation/deactivation of a lane change decision aid system function, and determining a warning condition of issuance/unissuance of the lane change decision aid system function based on a sensing result of the sensing unit; wherein the activation condition includes at least a continuous activation condition activating the lane change decision aid system function at all times when the subject vehicle starts, and wherein the warning condition includes at least one of: a blind spot warning condition issuing a blind spot warning when the target vehicle is located in the adjacent zones; a closing vehicle warning condition issuing a closing vehicle warning when the target vehicle is located in the rear zone and when a maximum closing speed and a collision time of the target vehicle satisfy a preset condition; and a forward vehicle warning condition issuing a forward vehicle warning when the target vehicle is located in the forward zone and a distance between the target vehicle and the subject vehicle is less than a preset distance; 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, and wherein the determination unit is additionally configured to determine a warning level evaluation condition for evaluating a warning level, and the warning level evaluation condition includes at least one of: a turn signal light evaluation condition determined as a high warning level when the driver turns on the turn signal light; and a steering input evaluation condition determined as the high warning level when the driver manipulates a steering of the subject vehicle, and wherein the preset condition includes maximum closing speed values of the target vehicle and collision time values corresponding to each maximum closing speed value. a sensing unit sensing whether there is a target vehicle in adjacent zones, a rear zone, or a forward zone of the subject vehicle; a determination unit determining an activation condition of activation/deactivation of a lane change decision aid system function, and determining a warning condition of issuance/unissuance of the lane change decision aid system function based on a sensing result of the sensing unit; wherein the activation condition includes at least a continuous activation condition activating the lane change decision aid system function at all times when the subject vehicle starts, and wherein the warning condition includes at least one of: a blind spot warning condition issuing a blind spot warning when the target vehicle is located in the adjacent zones; a closing vehicle warning condition issuing a closing vehicle warning when the target vehicle is located in the rear zone and when a maximum closing speed and a collision time of the target vehicle satisfy a preset condition; and a forward vehicle warning condition issuing a forward vehicle warning when the target vehicle is located in the forward zone and a distance between the target vehicle and the subject vehicle is less than a preset distance; 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, and wherein the determination unit is additionally configured to determine a warning level evaluation condition for evaluating a warning level, and the warning level evaluation condition includes at least one of: a turn signal light evaluation condition determined as a high warning level when the driver turns on the turn signal light; and a steering input evaluation condition determined as the high warning level when the driver manipulates a steering of the subject vehicle, and wherein the preset condition includes maximum closing speed values of the target vehicle and collision time values corresponding to each maximum closing speed value. a blind spot warning condition issuing a blind spot warning when the target vehicle is located in the adjacent zones; a closing vehicle warning condition issuing a closing vehicle warning when the target vehicle is located in the rear zone and when a maximum closing speed and a collision time of the target vehicle satisfy a preset condition; and a forward vehicle warning condition issuing a forward vehicle warning when the target vehicle is located in the forward zone and a distance between the target vehicle and the subject vehicle is less than a preset distance; 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, and wherein the determination unit is additionally configured to determine a warning level evaluation condition for evaluating a warning level, and the warning level evaluation condition includes at least one of: a turn signal light evaluation condition determined as a high warning level when the driver turns on the turn signal light; and a steering input evaluation condition determined as the high warning level when the driver manipulates a steering of the subject vehicle, and wherein the preset condition includes maximum closing speed values of the target vehicle and collision time values corresponding to each maximum closing speed value.