PURPOSE: To provide a dispersibility compensating element for the transmitting signals of an optical fiber so as to facilitate miniaturization, to reduce an inserting loss and to facilitate the control of a dispersing characteristic.

CONSTITUTION: A high frequency transmission line is formed by forming a coplanar center conductor (EuBa2Cu3Oy superconductor) 1 while folding plural linear parts and forming a ground conductor 2 at the remaining part by using a superconductor on an MgO substrate 3. A characteristic impedance at the corner of the part to be folded is increased rather than that of the linear part and the cyclic mismatching pat of the characteristic impedance is formed in the transmitting direction of the line. Thus, by using the superconductor for the conductor of the high frequency transmission line, the frequency dispersion caused by the conductor is eliminated so as to prevent the dispersion from being decreased by the structure and by changing the degree of the characteristic impedance mismatch or the like, the desired dispersing characteristic can be obtained. Further, by sufficiently reducing the high frequency loss of the superconductor, the inserting loss is decreased, the width of the line conductor can be reduced while keeping the inserting loss low at a certain degree and the element can easily be miniaturized.