A gate insulating film has a convex portion conforming to a surface shape of a gate electrode and a step portion that changes in height from a periphery of the gate electrode along the surface of the gate electrode. An oxide semiconductor layer is disposed on the gate insulating film so as to have a transistor constituting region having a channel region, a source region, and a drain region in a continuous and integral manner and a covering region being separated from the transistor constituting region and covering the step portion of the gate insulating film. A channel protective layer is disposed on the channel region of the oxide semiconductor layer. A source electrode and a drain electrode are disposed in contact respectively with the source region and the drain region of the oxide semiconductor layer. A passivation layer is disposed on the source electrode and the drain electrode.