The present invention provides a therapeutic agent for myotonic dystrophy which inhibits aberrant splicing responsible for myotonic dystrophy, resulting in an increase in a normally spliced product and thus improvement in a symptom of myotonic dystrophy, and is highly safe for use in long-term administration. The therapeutic agent for myotonic dystrophy comprises, as an active ingredient, at least one compound selected from the group consisting of erythromycin, clarithromycin and azithromycin, a pharmaceutically acceptable salt or hydrate thereof, or a prodrug thereof.
