PURPOSE: To measure the potential of wiring in the atmosphere in a non-contact manner by applying laser beam synchronous to an electric test pattern to a semiconductor integrated circuit provided with a phosphor layer molecularly oriented by the application of an electric field and measuring the intensity of the fluorescence from the phosphor layer.

CONSTITUTION: A phosphor 2 is applied to the surface of the semiconductor integrated circuit element 8 fixed to an X-Y stage 4 and a transparent electrode 1 and a press plate 7 are provided thereon in a close contact state. The element 8 is driven by a test pattern generating unit 5. The beam of a laser beam source 12 consisting of Ar laser for exciting the phosphor 2 and a pulse modulator and the light of an illumination light source 13 are synthesized to irradiate the surface of the element 8. At this time, laser beam is generated in synchronous relation to the clock cycle of the unit 5 to selectively irradiate the phosphor 2 at the specific wiring place of the element 8. The fluorescence from the phosphor 2 is converted to an electric signal by a photodetector 15 through a dichroic mirror 14 permitting light having the wavelength of said fluorescence to transmit.