The present invention addresses the problem of providing: a quality improver which has a proper molecular weight, a proper viscosity and solubility in cold water and can be used advantageously in the fields of foods, cosmetics, quasi drugs, drugs, industrial products, etc.; and a use of the quality improver. The problem can be solved by: a quality improver which can be produced by a production method involving a step of gelatinizing a waxy starch and then allowing an amylase to act on a gelatinized product to liquefy the gelatinized product and a step of allowing an α-glucosyltransferase to act on a liquefied product, and which contains an α-glucan mixture having the below-mentioned characteristic properties as an active ingredient; and a use of the quality improver: (1) the weight average molecular weight (Mw) falls within the range from 150 kDa to 3,000 kDa; (2) a value (Mw/Mn) obtained by dividing the weight average molecular weight (Mw) with a number average molecular weight (Mn) is 35.1 or less; and (3
