A method for manufacturing a thin film transistor substrate includes a step of forming a gate electrode (11a) and a first interconnect on a substrate (10), a step of forming a gate insulating film (12a) having a contact hole at a position overlapping the first interconnect, a step of forming a source electrode (13a) and a drain electrode (13b) overlapping the gate electrode (11a) and separated apart from each other, and a second interconnect connected via the contact hole to the first interconnect, a step of successively forming an oxide semiconductor film (14) and a second insulating film (15), and thereafter, patterning the second insulating film (15) to form an interlayer insulating film (15a), and a step of reducing the resistance of the oxide semiconductor film (14) exposed through the interlayer insulating film (15a) to form a pixel electrode (14b).