A plate conductor and at least three columnar conductors erected on the plate conductor are provided. At the same time when an electric field is measured by the plate conductor, two components of a magnetic field at the same measurement points as those at which the electric field is measured are measured by a loop formed by the plate conductor and the columnar conductors at the same time. As a result, three components of an electromagnetic field formed of one component of the electric field and two components of the magnetic field are measured at the same point, with high sensitivity, and at the same time.