This study attempts to speculate the dramatic construction of Shakespeare’s Twelfth Night which arranges diverse comic devices in pursuit of maintaining the gay mood of the play. These comic devices will be referred to as “comic guarantees.” The effective operation of comic guarantees―the fantasy world of Illyria, “unmasking” of the characters’ inner world through language, and the revelations of events to create “gaps of awareness”―is essential for ensuring the overall gaiety. This study renders the overview on comic guarantees, demonstrates the specific types and functions of comic guarantees, and then compares Twelfth Night with All’s Well That Ends Well, Shakespeare’s “dark” comedy. The comparative analysis of the two plays is to accentuate the effects of comic guarantees that the gay play, Twelfth Night, employs. (The Catholic University of Korea)