PURPOSE: To detect a defective picture element prior to the final assembling of a liquid crystal display by detecting the defect of a picture element electrode from the discoloration of the picture element electrode appearing by a chemical reaction among the picture element electrode, a signal line, a scanning line, etc., having respectively different ionization tendencies.

CONSTITUTION: A substrate is immersed in an electrolytic solution and the defect of the picture element electrode is detected from the discoloration of the picture element electrode appearing by the chemical reaction among the picture element electrode, the signal line, the scanning line, etc., having respectively different ionization tendencies. When a TFT base 5 for constituting a color liquid crystal display 5 is immersed in the electrolytic solution for instance, the picture element electrode 10 is discolored by the chemical reaction generated between the picture element electrode 10 and the signal line 12 having respectively different ionization tendencies. Consequently, a short part can be easily detected by visual observation as the discoloration of the electrode 10 and the short part can be repaired prior to the final assembling of the display.