Disclosed is a sustained release preparation which comprises an active ingredient having a higher release rate at pH 4 compared to that in pH 1.2 or pH6.8 and exerts a controlled release of the active ingredient in a pH-independent manner. The sustained release preparation comprises ethyl (-)-2-[4-[2-[[(1S,2R)-2-hydroxy-2-(4-hydroxyphenyl)-1-methylethyl]amino]ethyl]-2,5-dimethyl-phenoxy]acetate hydrochloride as the active ingredient and a pH-independent gel-forming polymer and contains substantially no pH-controlling agent other than the polymer. The sustained release preparation can release the active ingredient in a pH-independent manner in the range from 1.2 to 6.8 and shows a constant release rate for a prolonged period of time. Therefore, the preparation is useful as a therapeutic agent for frequent urination/incontinence of urine which has a long-lasting effect.
