To improve an S/N ratio in the inspection of an open failure and a short defect of each pixel of an LCD(Liquid Crystal Display) substrate by ten times or more of a conventional ratio.

A common grounding terminal 22 of an auxiliary capacitor of an LCD substrate 10 is grounded, and an H voltage from a driver 40 is applied to a video terminal 23 to open a gate of TFT(Thin Film Transistor) so that the auxiliary capacitor 15ij is charged to the maximum extent. Next, the gate is closed, and an L voltage of grounding electric potential is applied to the video terminal 23 so that a charge of floating capacity of a data line and a video line is discharged sufficiently. Then, each picture element is driven selectively and sequentially in a picture image display mode to read information of each pixel, convert it into a current and a voltage in an I-V conversion circuit 43, sample it in a sample-and-hole circuit 34, amplify it, and perform A/D conversion by an A/D converter 36 so that amplitude values are compared in a picture image processing part 37 to judge whether it is good or not.