The present invention provides a preparation containing pioglitazone or a salt thereof as an active ingredient, which shows high bioavailability of pioglitazone and less interindividual variation in blood drug concentration, as well as a preparation with suppressed color change during preservation. The preparation contains a core containing a pharmaceutically acceptable organic acid with water solubility at 20°C of not less than 10 mg/mL and pKa1 (a negative common logarithm of the first acid dissociation constant Ka1) at 25°C of not more than 5, and a coating layer containing pioglitazone or a salt thereof. The coating layer may further contain mannitol or trehalose.
