1. A movable body circumstance monitoring apparatus comprising: at least one means for capturing an image of a surrounding of a movable body depending upon movement of the movable body; means for deriving at least four feature points in a specified flat at the image captured by the at least one means for capturing the image; means for tracking the at least four feature points in response to movement of the movable body from a first state to a second state; and means for specifying moving condition such as relative position and posture of the at least one means for capturing the image at the first and second states in response to first flat coordinates of the feature points at the image captured at the first state and second flat coordinates of the feature points at the image at the second state based upon a tracking result by the means for tracking the at least four feature points.