PURPOSE: To change a characteristic impedance of a cable by composing a coaxial cable by providing a plurality of metal cylinder plates of a single one, double one, triple one, etc., coaxially, and grounding one of them for selecting the GND capacity.

CONSTITUTION: The capacity between metal cylinder plates 1 and 3 and the capacity between 3 and 5 are set to be different from each other, and the plates 1 and 5 are grounded, while the plate 3 is used for a signal line. Or otherwise, the plate 5 is grounded, and 1 is kept unprocessed, while the plate 3 is used for a signal line. Or 1 is grounded, and 5 is kept unprocessed, while 3 is used for a signal line, or 3 is grounded while 1 is used for a signal line, or 3 is grounded while 5 is used for a signal line. For changing the impedance, a relay or the like is used for increasing the quantity of the characteristic impedance to be selected. Insulation materials 2, 4 are put between the metal cylinder plates 1, 3, 5 respectively, and an insulation material 6 is also provided on the surface of the plate 5.