An apparatus for activating a pedestrian detection and collision mitigation system (PDCMS) of a vehicle, the apparatus comprising: a front detection sensor detecting of a presence of a pedestrian on a driving lane of the vehicle, gaze information of the pedestrian, and a distance and a relative speed between the pedestrian and the vehicle; a vehicle sensor detecting at least one of a speed, an acceleration, a steering angle, a steering angular velocity, or a pressure of a master cylinder of the vehicle; an electronic control unit determining whether to operate a PDCMS function based on information detected by the front detection sensor and the vehicle sensor; and a warning unit operated to inform a driver of a collision of the pedestrian with the vehicle by a control of the electronic control unit, wherein the front detection sensor includes: an image input processor acquiring an image in front of the vehicle; an ROI setting processor setting a region of interest corresponding to a size of an object in the image; a candidate extraction processor extracting a pedestrian candidate based on an operation of the object in the set ROI; and a pedestrian determination processor including a database and comparing the extracted pedestrian candidate with a posture of a sample pedestrian in the database to identify whether the extracted pedestrian candidate corresponds to the pedestrian, wherein the PDCMS function includes an activation of an operation of the warning unit and an activation of an operation of a brake regardless of whether the driver operates the brake, and wherein the activation of the operation of the warning unit and the activation of the operation of the brake are performed in an order of the operation of the warning unit, a partial braking of the vehicle, and a full braking of the vehicle, wherein the electronic control unit is further configured to determine that the function of the PDCMS is operated, if an absolute value of the initial speed of the pedestrian at the boundary of a driving lane is in a first speed range and the initial speed of the vehicle is in a second speed range at the time of determining whether the PDCMS function is operated, wherein the first speed range has a first minimum speed value and a first maximum speed value, and wherein the second speed range has a second minimum speed value and a second maximum speed value. a front detection sensor detecting of a presence of a pedestrian on a driving lane of the vehicle, gaze information of the pedestrian, and a distance and a relative speed between the pedestrian and the vehicle; a vehicle sensor detecting at least one of a speed, an acceleration, a steering angle, a steering angular velocity, or a pressure of a master cylinder of the vehicle; an electronic control unit determining whether to operate a PDCMS function based on information detected by the front detection sensor and the vehicle sensor; and a warning unit operated to inform a driver of a collision of the pedestrian with the vehicle by a control of the electronic control unit, wherein the front detection sensor includes: an image input processor acquiring an image in front of the vehicle; an ROI setting processor setting a region of interest corresponding to a size of an object in the image; a candidate extraction processor extracting a pedestrian candidate based on an operation of the object in the set ROI; and a pedestrian determination processor including a database and comparing the extracted pedestrian candidate with a posture of a sample pedestrian in the database to identify whether the extracted pedestrian candidate corresponds to the pedestrian, an image input processor acquiring an image in front of the vehicle; an ROI setting processor setting a region of interest corresponding to a size of an object in the image; a candidate extraction processor extracting a pedestrian candidate based on an operation of the object in the set ROI; and a pedestrian determination processor including a database and comparing the extracted pedestrian candidate with a posture of a sample pedestrian in the database to identify whether the extracted pedestrian candidate corresponds to the pedestrian, wherein the PDCMS function includes an activation of an operation of the warning unit and an activation of an operation of a brake regardless of whether the driver operates the brake, and wherein the activation of the operation of the warning unit and the activation of the operation of the brake are performed in an order of the operation of the warning unit, a partial braking of the vehicle, and a full braking of the vehicle, wherein the electronic control unit is further configured to determine that the function of the PDCMS is operated, if an absolute value of the initial speed of the pedestrian at the boundary of a driving lane is in a first speed range and the initial speed of the vehicle is in a second speed range at the time of determining whether the PDCMS function is operated, wherein the first speed range has a first minimum speed value and a first maximum speed value, and wherein the second speed range has a second minimum speed value and a second maximum speed value.