PURPOSE: To enable to compute impedance of respective conductors concisely and unerringly and lay a cable properly by displaying an arrangement location and phase designation of conductors and all other input data on a screen, and carrying out operation on a computer and displaying the computed results on the screen.

CONSTITUTION: Frequency, parallel number, conductor nominal sectional area or conductor diameter and horizontal distance and vertical distance between conductor centers are input to a computer waiting for input so as to be displayed on a screen such as CRT. Then, a previously inputted and stored arrangement list of conductor is displayed on the screen. The horizontal distance and the vertical distance between the conductor centers of this arrangement list are all expressed in a certain identical unit, and the horizontal distance 43 indicates that the horizontal distance between the adjoining conductor centers in a horizontal direction is 43 unit, and the vertical distance 43 indicates that the vertical distance between the adjoining conductor centers in a vertical direction is 43 unit. Next, the location of a conductor is designated by adding a mode sign in order to compute impedance. After the designation, the distance between respective conductor centers is computed.