To provide a heavy metal removing method for efficiently removing harmful heavy metal ions such as cobalt, nickel, lead, mercury or copper ion existing in a waste water in a minute quantity.

An aq. solution containing heavy metals is brought into contact with a polyolefin-based open cell foamed body composed of an amino acid fixed by radiation graft method. The polyolefin-based open cell foamed body is produced by molding a resin composition consisting of a polyolefin based resin containing ≥20 wt.% polyethylene-based resin (a) synthesized with a 4- valent transition metal and/or polyethylene based resin (b) having a density of <0.900 g/cm3 and ≥0.840 g/cm3, a thermal decomposable foaming agent, a cross-linking agent and a cross-linking assistant in non-cross-linking state and after that, heating under a normal pressure to simultaneously carry out the cross-linking and the foaming to form a cross-linked foamed body and mechanically deforming the foam in the cross-linked foamed body to communicate with each other.