A reagent preparing apparatus for preparing reagent by mixing a concentrated reagent and a diluting liquid and supplying the prepared reagent to a clinical sample measurement apparatus which measures a clinical sample using the supplied reagent, the reagent preparing apparatus comprising: a chamber for mixing the concentrated reagent and the diluting liquid; a liquid quality measurement part for measuring a quality of the diluting liquid; and a controller for controlling a flow of the diluting liquid based on the quality of the diluting liquid measured by the liquid quality measurement part is disclosed.