An apparatus for activating a pedestrian detection and collision mitigation system (PDCMS) of a vehicle, comprising: an engine management system, "EMS", for acquiring speed information on the vehicle in real time; an image collecting device for recognizing a pedestrian positioned within a driving lane of the vehicle and detecting information on a relative speed and a distance between the pedestrian and the vehicle, when a speed of the vehicle is equal to or greater than a set first speed; an electronic control unit, "ECU", for activating a PDCMS function based on a mapping table using the speed information on the vehicle and the information on a motion or the distance between the pedestrian and the vehicle, wherein a PDCMS activation state, in which the PDCMS function can be operated, is established when the speed of the vehicle is equal to or greater than a predetermined value Vmin and equal to or less than a predetermined value Vmax; and a warning device for informing a driver of a collision of the pedestrian with the vehicle by a control of the ECU, wherein the PDCMS function includes an activation of an operation of an active hood, an activation of an operation of the warning device, and an activation of an operation of a brake regardless of whether the driver operates the brake, wherein the activation of the operation of the brake regardless of whether the driver operates the brake is performed so that the speed of the vehicle is reduced to at least a predetermined speed or more from a time point when the operation of the brake is activated to a time point when the collision of the pedestrian with the vehicle occurs, wherein the mapping table is a data table comprising distance values between the pedestrian and the vehicle for determining the activation of the PDCMS function based on the distance between the pedestrian and the vehicle and whether the brake is operated by the driver, wherein in the mapping table, the distance between the vehicle and the pedestrian for determining the activation of the PDCMS function is longer when the brake is not yet operated by the driver than when the brake is already operated by the driver. an engine management system, "EMS", for acquiring speed information on the vehicle in real time; an image collecting device for recognizing a pedestrian positioned within a driving lane of the vehicle and detecting information on a relative speed and a distance between the pedestrian and the vehicle, when a speed of the vehicle is equal to or greater than a set first speed; an electronic control unit, "ECU", for activating a PDCMS function based on a mapping table using the speed information on the vehicle and the information on a motion or the distance between the pedestrian and the vehicle, wherein a PDCMS activation state, in which the PDCMS function can be operated, is established when the speed of the vehicle is equal to or greater than a predetermined value Vmin and equal to or less than a predetermined value Vmax; and a warning device for informing a driver of a collision of the pedestrian with the vehicle by a control of the ECU, wherein the PDCMS function includes an activation of an operation of an active hood, an activation of an operation of the warning device, and an activation of an operation of a brake regardless of whether the driver operates the brake, wherein the activation of the operation of the brake regardless of whether the driver operates the brake is performed so that the speed of the vehicle is reduced to at least a predetermined speed or more from a time point when the operation of the brake is activated to a time point when the collision of the pedestrian with the vehicle occurs, wherein the mapping table is a data table comprising distance values between the pedestrian and the vehicle for determining the activation of the PDCMS function based on the distance between the pedestrian and the vehicle and whether the brake is operated by the driver, wherein in the mapping table, the distance between the vehicle and the pedestrian for determining the activation of the PDCMS function is longer when the brake is not yet operated by the driver than when the brake is already operated by the driver.