A novel gasification process of waste plastics (WP) was investigated. The present paper shows principle of the gasification, especially role of a gasifying agent, experimental verification of effectiveness of the agent, and reaction scheme of the gasification. The gasifying agent of WP, that is most characteristic feature of this process, is a mixed gas mainly composed of CO₂, H₂, and H₂O and easily produced by the water gas shift reaction of a by-product gas generated in steelmaking process. By fluidized-bed micro reactor experiments, lower heating value (LHV) of the gas produced by the gasification of low-density polyethylene (LDPE) and WP was 22.5 MJ/Nm³ and 19.3 MJ/Nm³, respectively, with 66% of gas yield for LDPE and 56% for WP at atmospheric pressure and 873K with a nickel powder catalyst diluted by silica sand. It was concluded that not only polyolefins but also other various polymers such as polyesters and elastomers were gasified based on polymer components included in WP and the gas yield of WP. The gasification reaction scheme was also discussed.