PURPOSE: To enable the measurement of magnetic permeability at a high frequency band by arranging a magnetic body on the surface of a conductor directly or through a non-magnetic body.

CONSTITUTION: A magnetic body 2 is made in strips and is arranged on the surface of a conductor 3 through a non-magnetic body 4 so as to encircle the conductor 3 to form a line 1. Then, reflection factors at one end of the line 1, a reflection factor at the other end thereof and a permeation efficient to the other end from one end thereof are measured when a magnetic field large, sufficiently as compared with an anisotropic magnetic field of the magnetic body 2. These parameters measured are used to determine a frequency characteristic of a specified magnetic permeability of the magnetic body 2. Thus, the use of a transmission line eliminates resonance phenomenon in a measuring system thereby enabling the measurement of a magnetic permeability at a high frequency band exceeding 100MHz. When the non-magnetic band 4 is removed and the magnetic body 2 is arranged direct on the surface of the conductor 3, the same effect is obtained.