A flocculant for separating and flocculating oily components and water components is provided so that no sludge is produced when the oily components and the water components contained in the emulsion having a high COD value; and the throughput of the active sludge is not decreased in the secondary treatment of the active sludge. A flocculant for separating and flocculing oily components and water components contained in oil-in-water type or water-in-oil type emulsion, comprises a unit (i), and at least one of units (ii) and (iii) represented by the following formulas: (i) --(C(R.sub.1R.sub.2)C(R.sub.3X))--, (ii) --(C(R.sub.4R.sub.5)C(R.sub.6Y))--, (iii) --(C(R.sub.7R.sub.8)C(R.sub.9Z))--; wherein X is a group having --SO.sub.3M, M is hydrogen or a metal element, Y is a group having a quaternary nitrogen atom, Z is an electrophilic group, each R.sub.1 to R.sub.9 is hydrogen or an alkyl group, and a ratio per molecule of these units (i):(ii):(iii) is (1 to 100):(1 to 100):(1 to 100).