A process is developed for recycling a polyolefin cross-linked substance having a cross-linkage, a polyolefin foamed substance free from a cross-linkage or a polyolefin foamed substance having a cross-linkage. The process includes the step of heating the polyolefin cross-linked substance together with a cross-linkage breaking agent, whereby breaking the cross-linkage to recycle the polyolefin cross-linked substance into a moldable thermoplastic resin. Further, the process includes the step of adding a foaming-agent-decomposition facilitating agent to the polyolefin foamed substance in the course of thermally melting the polyolefin foamed substance, whereby decomposing a residual foaming agent remaining in the polyolefin foamed substance. Furthermore, the process includes the step of adding a foaming-agent-decomposition facilitating agent to the polyolefin foamed substance in the course of heating the polyolefin foamed substance to break the cross-linkage, whereby decomposing a residual foaming agent remaining in the polyolefin foamed substance. The resulting recycled product is improved in terms of moldability, strength, elongation and superficial appearance.