Provided are an extract, which is a fractionated component 1 of a water extract of a plant powder, wherein the fractionated component 1 is a fractionated component having a fractionation molecular weight of 12,000 or greater, wherein an ethanol-undissolved component of the fractionated component 1 exhibits a peak attributable to carboxylic acid in a Fourier transform infrared spectroscopy (FT-IR) measurement and exhibits a peak attributable to cellulose in a gas chromatography mass spectrometry (GC-MS) measurement, and wherein an ethanol-dissolved component of the fractionated component 1 exhibits a peak attributable to carboxylic acid in the FT-IR measurement and exhibits a peak attributable to a plant protein in the GC-MS measurement, and a water-purifying agent containing the extract.