Disclosed are a thin film transistor substrate where barrier metal can be omitted to be formed between a semiconductor layer of a thin film transistor and source and drain electrodes (barrier metal need not be formed between the semiconductor layer of the thin film transistor and the source and drain electrodes), and a display device. (1) A thin film transistor substrate has a semiconductor layer of a thin film transistor, a source electrode, a drain electrode, and a transparent conductive film, wherein the substrate has a structure in which the source and drain electrodes are directly connected to the semiconductor layer of the thin film transistor, and the source and drain electrodes include an Al alloy thin film containing Ni of 0.1 to 6.0 atomic percent, La of 0.1 to 1.0 atomic percent, and Si of 0.1 to 1.5 atomic percent. (2) A display device has the thin film transistor substrate.