Abstract: A thin film transistor includes: a gate electrode; a gate insulting film formed on the gate electrode; an oxide semiconductor thin film layer forming a channel region corresponding to the gate electrode on the gate insulating film; a channel protective layer that is formed at least in a region corresponding to the channel region on the gate insulating film and the oxide semiconductor thin film layer, and that includes a first channel protective layer on a lower layer side and a second channel protective layer on an upper layer side; and a source/drain electrode that is formed on the channel protective layer and is electrically connected to the oxide semiconductor thin film layer. The first channel protective layer is made of an oxide insulating material, and one or both of the first channel protective layer and the second channel protective layer is made of a low oxygen permeable material.