Provided is an elastic fiber treatment agent, containing; a hydrocarbon resin (A); and a hydrocarbon oil (B). The hydrocarbon resin (A) contains a polymer having a structural unit, as a main structural unit, derived from at least one monomer selected from aromatic olefin and aliphatic diolefin, the polymer being partially hydrogenated or fully hydrogenated. It is preferred that the hydrocarbon resin (A) contains a polymer having a structural unit derived from aromatic olefin as a monomer, the polymer being partially hydrogenated or fully hydrogenated, and the aromatic olefin is at least one selected from indene and methylstyrene. Thus, the elastic fiber treatment agent of the present invention imparts excellent unraveling properties to elastic fibers and has excellent adhesiveness to hot melt adhesives, enables the production of stretchable sheets exhibiting good adhesiveness even when processed at a high draft ratio, and is suitable for obtaining soft feel sanitary products.