The present invention relates to powder detergent granules that are substantially free of a water-insoluble component such as zeolite or silica, a method for manufacturing the powder detergent granules and a copolymer having various properties useful as a detergent component. The powder detergent granules of the present invention are substantially free of a water-insoluble component, and thus exhibit good solubility and washing performance (stain removal performance) in cold water, do not leave residue after laundry, and reduce the likelihood of a caking phenomenon during manufacture and storage. And, the powder detergent granules of the present invention are substantially free of zeolite or silica that absorbs a liquid component, but are capable of accommodating a considerable amount of liquid surfactant. Further, a copolymer comprising acrylic acid monomer unit and 2-acrylamido-2-methylpropane sulfonic acid monomer unit, an acidic water-soluble polymer of the present invention, is useful as a detergent component in various aspects.