To provide flexibility, elasticity and high shaping properties, apply smoothly to the curved surface forming for a cubic curved surface and carry out the easy manufacture.

Thid honeycomb core 9 is composed of a plane aggregate of cells 10 of a hollow column shape divided and formed by cell walls 7, and plane surfaces of a sectional straight line shape are not formed by respective cell walls 7 among bonded sites, and at least one wall section 8 of sectional folded line shape is provided on one cell wall. In this manufacturing process by the conventional spreading process for the honeycomb core 9, the temporary bonding by a second bonding material 6 having the bonding force inferior to that of a conventional first bonding material 3 is added, and folded sections 8 are made to remain on the cell walls 7 by utilizing plastic deformation of traces of released temporary bonding during the spreading. The shrinkage deformation and stretch deformation inside and outside are carried out smoothly at the time of curved surface forming for the honeycomb core 9.