The present invention relates to a method for selecting an installation position of a link antenna of an in-building RF repeater, a cable device thereof, and a terminal. The method selects the position for measuring the greatest Ec/Io by using directivity of the link antenna in an area for installing the link antenna. The link antenna is installed at the selected position. The direction with the greatest Ec/Io that is measured by using directivity of the link antenna is fixed to be a desired direction from among target directions to be directed by the link antenna. In this instance, measurement of Ec/Io by using directivity of the link antenna is performed by a mobile station connected to the link antenna through an access cable. Accordingly, the link antenna can be installed at the optimized position and in the optimized direction. Hence, the Ec/Io within the building is substantially reduced.