A sliding property improver for use in washing which comprises potassium metaphosphate; a detergent composition comprising said sliding property improver for use in washing and a solubilizing agent; a method of washing by hand which comprises carrying out under a condition wherein a concentration of potassium metaphosphate is 30 mg/L or more and a liquor-goods ratio is 2 or more; a sliding property improver granule for use in washing which comprises potassium metaphosphate; and a detergent composition comprising said sliding property improver granules for use in washing and a solubilizing agent. The above sliding property improver for use in washing and the sliding property improver granule for use in washing are suitably used also in washing clothes or the like by hand, in particular, that involving immersion for a long time.