An active object detection sensor that operates to form a detection area by a transmission area having a plurality of division areas and a reception area having a plurality of division areas, wherein the transmission area and the reception area are overlaid on each other to form the detection area, and to detect an object in the detection area, the active object detection sensor comprising: a plurality of transmitter elements each configured to transmit detection rays for object detection sequentially, to the transmission area; a plurality of receiver elements each configured to receive the detection ray reflected by the object from the reception area; and an optical divider (7,8) disposed, in front of the transmitter elements and/or the receiver elements, wherein the optical divider, so disposed on a transmission side and/or a reception side, has a plurality of optical dividing pieces (7S, 8S) each having a plurality of optical deflection surfaces (7a, 7b, 8a, 8b) on which an angle of the detection ray is varied to a plurality of angles for dividing the detection ray toward the plurality of division areas, each of the optical deflection surfaces in the optical dividing pieces on the transmission side and/or the reception side being set to have a given angle, so as to assign the detection ray from the transmitter elements and/or the detection ray toward the receiver elements, to a given division area, such that a combination of the transmitter elements and the receiver elements forming one of the division areas is different from a combination of the transmitter elements and the receiver elements forming another one of the division areas, characterised in that detection rays from the plurality of transmitter elements or detection rays toward the plurality of receiver elements are assigned to a given area among the division areas, so as to partially form the division area in which detection rays from the plurality of transmitter elements are overlaid on each other in the transmission area or detection rays toward the plurality of receiver elements are overlaid on each other in the reception area. a plurality of transmitter elements each configured to transmit detection rays for object detection sequentially, to the transmission area; a plurality of receiver elements each configured to receive the detection ray reflected by the object from the reception area; and an optical divider (7,8) disposed, in front of the transmitter elements and/or the receiver elements, wherein the optical divider, so disposed on a transmission side and/or a reception side, has a plurality of optical dividing pieces (7S, 8S) each having a plurality of optical deflection surfaces (7a, 7b, 8a, 8b) on which an angle of the detection ray is varied to a plurality of angles for dividing the detection ray toward the plurality of division areas, each of the optical deflection surfaces in the optical dividing pieces on the transmission side and/or the reception side being set to have a given angle, so as to assign the detection ray from the transmitter elements and/or the detection ray toward the receiver elements, to a given division area, such that a combination of the transmitter elements and the receiver elements forming one of the division areas is different from a combination of the transmitter elements and the receiver elements forming another one of the division areas, characterised in that detection rays from the plurality of transmitter elements or detection rays toward the plurality of receiver elements are assigned to a given area among the division areas, so as to partially form the division area in which detection rays from the plurality of transmitter elements are overlaid on each other in the transmission area or detection rays toward the plurality of receiver elements are overlaid on each other in the reception area.