A nitride semiconductor device includes the followings. A semiconductor multilayer structure is above a substrate and includes a first nitride semiconductor layer and a second nitride semiconductor layer. A source electrode, a drain electrode, and a gate electrode are on the semiconductor multilayer structure. A gate wiring line transmits a gate driving signal to gate electrodes. A first shield structure is on the semiconductor multilayer structure between the drain electrode and the gate electrode or between the drain electrode and the gate wiring line in a non-channel region where an actual current path from the drain electrode to the source electrode is not formed in the semiconductor multilayer structure. The first shield structure is a normally-off structure, suppresses a current flowing from the semiconductor multilayer structure, and is set to have a substantially same potential as a potential of the source electrode.