To provide an active matrix substrate and its manufacturing method in which large area of silicon remaining becomes a black point defect and small area of silicon remaining can be certainly detected by a detector even when the silicon remaining occurs in a manufacturing process of an active matrix substrate.

A Cr film 16 is formed in advance in a pixel electrode region large area of which is occupied by pixels simultaneously with formation of a source/drain electrode. Then an ITO film 7 is formed so as to be in direct contact with the Cr film 16 and the ITO film 7 is subjected to wet etching by using ammonium cerium (IV) nitrate (NH4)2Ce(NO3)6 and nitric acid HNO3. When the silicon remaining 24 occurs below the Cr film 16 by extending between wiring 16 and wiring 36 at this time, the Cr film 16 on the silicon remaining 24 remains due to galvanic action of an etching solution and thereby resistance between wiring is reduced and detection of short circuit between wiring is facilitated.