To provide an E-O probe which can measure a voltage distribution in a fine region while enlarging it. A grounded, transparent electrode 2 and an electrooptic member 3 such as LiTaO.sub.3 are successively fixed to and below a support 1. There are a plurality of conical, conductive members 5a-5e arranged below a reflection film 4 in such a manner that the bottom surfaces thereof are fixed to the lower surface of the reflection film 4 and that the lower ends thereof project downward. Spaces between the plural, linear, electric needles 5a-5e become narrower toward a measured object located below them, whereby voltages in a fine region in the measured object can be guided as enlarged to the electrooptic member 3.