A movable body circumstance monitoring apparatus includes element for
capturing an image of a surrounding of a movable body depending upon
movement of the movable body, deriving at least four feature points in a
specified flat at the image, tracking the feature points in response to
movement of the movable body from a first state to a second state, and
specifying relative position and posture of the element for capturing the
image at the first and second states in response to first flat
coordinates of the feature points at the first state and second flat
coordinates of the feature points at the second state based upon a
tracking result.