To provide a method for producing a biodegradable resin foam having a high foaming ratio and capable of being degraded under composting environments and capable of being photo-degraded.

This method for producing a biodegradable resin foam comprises mixing and kneading starch, an aromatic ketone, a polyolefin resin, a foaming agent and a cross-linking agent, thermally foaming the obtained foamable cross- linkable composition in a non-closed mold, and then mechanically deforming the obtained foam to open the cells.