An object detector comprising: an optical scanning system including a light source with N, where N ≥ 2, light emitting areas (A) disposed apart from each other in at least one direction, wherein the optical scanning system is configured to scan a scanning range with light output from the light source , wherein the scanning range is in a scanning direction differing from the at least one direction; and a light-receiving system including k, where k ≥ 1, light-receiving units configured to receive light emitted from the optical scanning system and reflected from an object, wherein the scanning range to be scanned by the optical scanning system is divided in the scanning direction into M, where M ≥ 2, fields, and the optical scanning system is configured to scan m, where m ≥ 1, fields out of the M fields in T that is a time period for scanning the scanning range in one scan, and wherein n, where n ≥ 1, light emitting areas (A) out of the N light emitting areas (A) are configured to sequentially emit light to each of the m fields at an interval of T / (m × n) in a time period of T / m; wherein a conditional expression below is satisfied: T / m × n > 2 L max / c × k where L max is a maximum detection distance of the object, and c is a speed of light, and wherein m is a submultiple of M; wherein the n light emitting areas (A) are 1 st through n-th light emitting areas that are disposed in the at least one direction, wherein n is expressed by 2p where p is a natural number, and wherein one of the 1 st through p-th light emitting areas and one of the (p + 1)th through 2p-th light emitting areas are not adjacent to each other and are configured to sequentially emit light when the n light emitting areas (A) sequentially emit light to each of the m fields in the time period of T / m. an optical scanning system including a light source with N, where N ≥ 2, light emitting areas (A) disposed apart from each other in at least one direction, wherein the optical scanning system is configured to scan a scanning range with light output from the light source , wherein the scanning range is in a scanning direction differing from the at least one direction; and a light-receiving system including k, where k ≥ 1, light-receiving units configured to receive light emitted from the optical scanning system and reflected from an object, wherein the scanning range to be scanned by the optical scanning system is divided in the scanning direction into M, where M ≥ 2, fields, and the optical scanning system is configured to scan m, where m ≥ 1, fields out of the M fields in T that is a time period for scanning the scanning range in one scan, and wherein n, where n ≥ 1, light emitting areas (A) out of the N light emitting areas (A) are configured to sequentially emit light to each of the m fields at an interval of T / (m × n) in a time period of T / m; wherein a conditional expression below is satisfied: T / m × n > 2 L max / c × k where L max is a maximum detection distance of the object, and c is a speed of light, and wherein m is a submultiple of M; wherein the n light emitting areas (A) are 1 st through n-th light emitting areas that are disposed in the at least one direction, wherein n is expressed by 2p where p is a natural number, and wherein one of the 1 st through p-th light emitting areas and one of the (p + 1)th through 2p-th light emitting areas are not adjacent to each other and are configured to sequentially emit light when the n light emitting areas (A) sequentially emit light to each of the m fields in the time period of T / m. <EOS>