An object detection apparatus comprising: a light illumination unit configured to emit illuminating light for illuminating a monitoring area defined on a light transmissive member; an imaging unit including an image sensor, the image sensor having a first light receiving area and a second light receiving area, the imaging unit being configured to capture a first image of distant photographic subjects by detecting, in the first light receiving area, lights from the distant photographic subjects that pass through the light transmissive member, to capture a second image of foreign matter attached to the monitoring area on the light transmissive member by detecting, in the second light receiving area, the illuminating light reflected from the foreign matter and passing through the light transmissive member, and to generate an image frame including the first image and the second image; a target detection unit configured to detect a detection target among the distant photographic subjects based on the first image in the imaging frame; and a foreign matter detection unit configured to detect the foreign matter adhered to the monitoring area on the light transmissive member based on the second image in the imaging frame; characterised in that the apparatus further comprises an exposure amount change unit configured to change an exposure amount of the imaging unit from imaging frame to imaging frame in a serial and repetitive manner; wherein the target detection unit detects the detection target using the first images in two or more of the imaging frames which have different exposure amounts to each other, and the foreign matter detection unit detects the foreign matter using the second image in an imaging frame of the two or more imaging frames, other than an imaging frame with a greatest exposure amount among the two or more imaging frames. a light illumination unit configured to emit illuminating light for illuminating a monitoring area defined on a light transmissive member; an imaging unit including an image sensor, the image sensor having a first light receiving area and a second light receiving area, the imaging unit being configured to capture a first image of distant photographic subjects by detecting, in the first light receiving area, lights from the distant photographic subjects that pass through the light transmissive member, to capture a second image of foreign matter attached to the monitoring area on the light transmissive member by detecting, in the second light receiving area, the illuminating light reflected from the foreign matter and passing through the light transmissive member, and to generate an image frame including the first image and the second image; a target detection unit configured to detect a detection target among the distant photographic subjects based on the first image in the imaging frame; and a foreign matter detection unit configured to detect the foreign matter adhered to the monitoring area on the light transmissive member based on the second image in the imaging frame; characterised in that the apparatus further comprises an exposure amount change unit configured to change an exposure amount of the imaging unit from imaging frame to imaging frame in a serial and repetitive manner; wherein the target detection unit detects the detection target using the first images in two or more of the imaging frames which have different exposure amounts to each other, and the foreign matter detection unit detects the foreign matter using the second image in an imaging frame of the two or more imaging frames, other than an imaging frame with a greatest exposure amount among the two or more imaging frames.