The present invention provides a treating agent for polyolefin synthetic fiber, an aqueous liquid of the treating agent, a method of treating polyolefin synthetic fiber using the aqueous liquid, a polyolefin synthetic fiber having the treating agent adhered thereto, and a thermally-bonded nonwoven fabric made of the polyolefin synthetic fiber. The treating agent for polyolefin synthetic fiber is capable of keeping a good antistatic property or card passability and endows the obtained nonwoven fabric with a high hydrophilicity. Also, the nonwoven fabric can be adjusted to be weakly acidic.The treating agent for polyolefin synthetic fiber as used comprises: 0.3-18 mass% of a specific organic acid, 10-50 mass% of an alkyl phosphoric acid ester salt B having 4-11 carbon atoms, 10-50 mass% of an alkyl phosphoric acid ester salt C having 12-22 carbon atoms, and 25-65 mass% of a specific polyoxyalkylene derivative, based on a total of 100 mass%, and a specific aqueous liquid has a pH of 3 or above and less than 7.本發明提供一種聚烯烴系合成纖維用處理劑、該處理劑之水性液、使用該水性液之聚烯烴系合成纖維之處理方法、附著有該處理劑之聚烯烴系合成纖維及該聚烯烴系合成纖維製之熱黏不織布，上述聚烯烴系合成纖維用處理劑可維持良好之制電性或梳棉機通過性，並且對所得之不織布賦予高度之親水性，另外可將不織布調整為弱酸性。作為聚烯烴系合成纖維用處理劑，使用如下者：以0.3~18質量%之比例含有特定之有機酸，以10~50質量%之比例含有碳數為4~11之烷基磷酸酯鹽B，以10~50質量%之比例含有碳數為12~22之烷基磷酸酯鹽C，及以25~65質量%之比例含有特定之聚氧伸烷基衍生物(合計100質量%)，且特定之水性液之pH值為3以上且未滿7。
