A nitride semiconductor substrate including a group III nitride semiconductor crystal and having a main surface, wherein a low index crystal plane is (0001) plane curved in a concave spherical shape to the main surface, and the off-angle (θm, θa) at a position (x, y) in the main surface approximated by x representing a coordinate in a direction along axis, y is a coordinate in a direction along axis, (0, 0) represents a coordinate (x, y) of the center, θm represents a direction component along axis in an off-angle of axis with respect to a normal, θa represents a direction component along axis in the off-angle, (M1, A1) represents a rate of change in the off-angle (θm, θa) with respect to the position (x, y) in the main surface, and (M2, A2) represents the off-angle (θm, θa) at the center.