To provide a technique of increasing a radius of curvature of (0001) plane, and narrowing an off-angle distribution, there is provided a nitride semiconductor substrate containing a group III nitride semiconductor crystal and having a main surface in which a nearest low index crystal plane is (0001) plane, wherein (0001) plane in one of a direction along axis and a direction along axis orthogonal to the axis, is curved in a concave spherical shape with respect to the main surface, and a radius of curvature of the (0001) plane in one of the direction along the axis and the direction along the axis orthogonal to the axis is different from a radius of curvature of at least a part of the (0001) plane in the other direction.