To provide a water-soluble processing oil hardly exerting influence of corrosion or the like on aluminum or an alloy thereof, and effectively preventing the emulsification of lubricant oil, hydraulic fluid or the like mixed when using the processing oil.

The water-soluble processing oil contains a cationic demulsifier and at least one alkylsulfonic acid compound represented by general formula (1) (wherein, R1 is a 5-11C linear or branched alkyl group or alkylene group, or a linear or branched alkyl group or alkylene group containing an aromatic ring; both of R2 and R3 are hydrogen, or one of R2 and R3 is hydrogen and the other is a 1-4C linear or branched alkyl group or alkylene group) or a salt thereof.