The present invention provides a nonaqueous electrolyte secondary battery insulating porous layer having an excellent withstand voltage property and an excellent leakage resistance characteristic. The nonaqueous electrolyte secondary battery insulating porous layer having a trabecular structure including voids, which trabecular structure has an anisotropy value of 1.30 to 2.10, the anisotropy value being calculated from a three-dimensional image showing a void part and a solid content part on respective two gradation levels, the three-dimensional image being prepared by analyzing images of cross sections obtained by making observation at intervals of 20 nm in a thickness direction from a surface of the nonaqueous electrolyte secondary battery insulating porous layer with use of a FIB-SEM having a magnification of 6500 times.