To provide a modified foaming agent prepared by coating a surface of a foaming agent powder with a metal siloxane-based compound.

The modified foaming agent is excellent in dispersibility in a resin when added into a polymer resin, and increases productivity and workability by improving flowing properties of the polymer resin in a processing using an extruder and an injector, and a foamed article produced by using the modified foaming agent has a fine and uniform forming cells, and increasing of cell number per unit surface area realizes excellency in tear strength, durability, and sound insulation characteristics.