To adjust a bending flexibility of a packaging cushioning material A of an angular tubular shape that is formed from a top plate 1, right and left side plates 2 and 3 and a bottom plate 4, and that is bent so as to intersect at least part of each of the side plates 2 and 3 in the height direction, so as to be vertically flexibly bent on account of the elasticity of folds 5a to 5f, and so as to have an inward V shape in a vertical cross section.

A sub-flexible section 106 the vertical cross-section of which includes an outward V-shape is defined by reversely bending a cushioning material along each two cuts 103 vertically intersecting a fold extending through the apex of the inward V shape of the vertical cross-section and along folds 105 formed between the upper ends and lower ends of the two cuts 103 on the same side.