A flavor improving agent which contains, as the active ingredient, a milk serum mineral satisfying all of the following requirements (a), (b), (c), (d) and (e): (a) the ash content of the solid matters in the milk serum mineral being from 25 to 75% by mass; (b) the calcium content of the solid matters in the milk serum mineral being less than 2% by mass; (c) the calcium content of the ash in the milk serum mineral being less than 5% by mass; (d) the lactic acid content of the solid matters in the milk serum mineral being 1.0% by mass or more; and (e) the pH value of a 0.1% by mass aqueous solution of the solid matters in the milk serum mineral being from 6.0 to 7.5.