A binocular robot vision system having an autonomously moving active viewpoint is proposed. By using this active viewpoint, the system constructs a correspondence between the images of a feature points on the right and left retinas easily and calculates the spatial coordinates of the feature points. The system incorporates two intelligent functions for enlarging the measuring region and increasing the accuracy of measurement. The first intelligent function is an autonomous movement of the viewpoint and the second is weighting process for measured points. These functions work when the system can recognize the solid body. As the first steps of the development of the recognition of a solid body, we incorporate these functions into the system to detect straight lines in an image. To detect lines we use Hough transform. The system searches a region surrounded by 4 straight lines. Then the system recognizes the region as a quadrangle. The system constructs a correspondence between the quadrangles in the right and left images. By the use of the result of the constructed correspondence, the system calculates the spatial coordinates of an object. An experiment shows the effect of the line detection using Hough transform, the recognition of the surface of the object and the calculation of the spatial coordinates of the object.