PROBLEM TO BE SOLVED: To easily measure the moisture content in a medium as a component not affected by the kind of the medium and an element such as salt or the like contained in the medium.
SOLUTION: A fold-back parallel two-line transmission passage is arranged in the medium and the i-th frequency signal Si having the i-th frequency fi is supplied to the signal input terminal thereof. The i-th frequency signal Si and the i-th frequency signal Si' based on the i-th frequency signal Si obtained from the signal output terminal of the folded parallel two-line transmission passage are used to form the i-th phase difference display data Di showing the phase difference between them and this data Di is used to form the i-th dielectric constant display data Ei showing the dielectric constant of the medium and a plurality of dielectric constant display data E1, E2, etc. formed by setting i to 1, 2, etc. are used to form dielectric constant display data E0 showing a dielectric constant having no frequency dependence of the medium while this dielectric constant display data E0 is used to form moisture content display data showing the moisture content of the medium.