ELECTRIC FIELD DETECTOR

PURPOSE:To directly measure a voltage across electrodes without causing resonance even at a high frequency in a device wherein an electro-optical element which changes an optical characteristic when an electric field is applied is arranged so as to be close to a circuit board to be measured and a change in the optical characteristic is measured by an optical beam. CONSTITUTION:An auxiliary electrode 5 is installed on the surface of an electro- optical element 1, and a connecting electrode 6 which is used to connect it to a reference electrode 32 on a circuit board 2 to be measured is provided. Consequently, a voltage across an electrode 31 to be measured and the reference electrode 32 is applied effectively to the electro-optical element 1, and its sensitivity is increased. In addition, the voltage of the electrode 31 to be measured with reference to the reference electrode 32 can be measured irrespective of the geometrical arrangement of the electrode 31. In addition, since a connecting wire is not drawn, the title device is not resonated even at a high frequency.