The present invention provides a pharmaceutical composition for treating or preventing cancer, containing, as an active ingredient, a compound having a specific chemical structure and an activity of inhibiting the formation of a c-Myc/Max/DNA complex, or a pharmaceutically acceptable salt thereof. The present invention provides a medical use of the pharmaceutical composition, according to the present invention, for treating or preventing cancer. The present invention also provides a method for treating or preventing cancer, comprising administering, to a subject in need of treatment, an effective amount of the compound, the salt thereof, or the composition, according to the present invention, containing both the compound and the salt thereof.