This paper proposes a calibration method of a distributed vision network in a unified world coordinate system. The vision network system is conceived to support a robot working in our daily human life environment: the system provides with visual observation of the dynamically changing situation surrounding the robot. Vision cameras are rather sparsely distributed to cover a wide area such as a block of a town. Position, view direction and range of view are the camera parameters of principal importance to be estimated by the proposed method. A set of calibration data for each distributed camera is provided by a group of mobile robots having a cooperative positioning function and visually distinguishable markers mounted on the body of the robot.