An information processor acquires a stereo image from an imaging device. A detection plane definition portion defines a detection plane in a three-dimensional space of a camera coordinate system of a first camera. A feature quantity calculation portion generates feature point image of left and right images. A parallax correction area derivation portion derives an area as a parallax correction area, which is obtained by moving, to a left, an area of the right image identical to the detection area of the left image. A matching portion performs matching for the feature point images of each area, thus deriving a highly rated feature point. A position information output portion generates information to be used by an output information generation section based on the matching result.