An object detecting system includes stereo-image taking means for taking images of an object and outputting the images as a reference image and a comparative image, stereo matching means for calculating parallaxes by stereo matching, and determination means for setting regions of objects in the reference image on the basis of the parallaxes grouped by grouping means, and performing stereo matching again for an area on the left side of a comparative pixel block specified on an epipolar line in the comparative image corresponding to a reference pixel block in a left end portion of each region. When a comparative pixel block that is different from the specified comparative pixel block and provides the local minimum SAD value less than or equal to a threshold value is detected, the determination means determines that the object in the region is mismatched.