The present invention relates to a pharmaceutical preparation containing an active ingredient and a release-controlling agent for adjusting the release of the active ingredient, in which the active ingredient is at least one selected from among mirabegron and a pharmaceutically acceptable salt thereof, and the release-controlling agent is a hydrogel-forming polymer, the hydrogel-forming polymer being at least one selected from among polyethylene oxide, hydroxypropyl methyl cellulose, hydroxypropyl cellulose, sodium carboxymethylcellulose, and hydroxyethyl cellulose and having an average molecular weight ranging from 100,000 to 8,000,000. The present invention is capable of suppressing the generation of impurities therein and of effectively controlling the release of at least one selected from among mirabegron and a pharmaceutically acceptable salt thereof.