A device for manufacturing an active matrix substrate including a plurality of pixels arranged in a matrix, in which a short-circuit defect in the active matrix substrate is detected and repaired, includes a stage (30a) configured to place a test substrate (19) which will become the active matrix substrate, a defective pixel detector (40a) configured to input a test signal to the test substrate (19) placed on the stage (30a), and electrically detect coordinates of a defective pixel in which a short-circuit defect has occurred, and a defect position identifier (50) configured to input the test signal to the test substrate (19) placed on the stage (30a) to cause the defective pixel detected by the defective pixel detector (40a) to generate heat, and sense the heat generation in the defective pixel using far-infrared thermography, thereby identifying a position of the short-circuit defect in the defective pixel.