PURPOSE: To test a matrix of thin film transistor(TFT) used for an active matrix liquid crystal display panel by performing probe inspection for a slight number of terminals that can be accessed.

CONSTITUTION: An AC signal 26 which is in series with a variable DC power source 34 drives gate lines of an LCD display driving matrix and ammeters 28 and 32 monitor currents generated on drain lines. Consequently, measured admittance when the value of the DC power source output is made usable is compared with that when unusable to conduct a test about whether or not the matrix 10 has a defect.