Each thin film transistor of an active matrix substrate includes an oxide semiconductor layer, a gate electrode disposed closer to the substrate side of the oxide semiconductor layer, a gate insulating layer, a source electrode, and a drain electrode, wherein the oxide semiconductor layer includes a layered structure including a first layer and a second layer disposed on a part of the first layer and extending across the first layer in a channel width direction when viewed in a normal direction of the substrate, the first layer includes an overlapping portion overlapping with the second layer, and a first portion and a second portion each located on a corresponding one of both sides of the second layer, when viewed in a normal direction of the substrate, the second layer covers an upper surface and a side surface of the overlapping portion of the first layer, the source electrode is electrically connected to at least a part of an upper surface of the first portion, and the drain electrode is electrically connected to at least a part of an upper surface of the second portion.