This conversation analytic study investigates the use of the Japanese contrastive marker "demo" "but" as a preface to responses to polar questions. "Demo"-prefaced responses are one type of nonconforming answers, that is, responses that provide (dis)affirmation to preceding questions without yes/no-tokens. This study explores how question recipients treat the preceding questions with their "demo"-prefaced responses. The data analysis is twofold: this research first examines the turn-initial "demo" to scrutinize basic properties of "demo"-prefacing in responses to polar questions; then the study explores how the basic properties are in effect with "a" + "demo"-prefacing (i.e., "demo"-prefacing preceded by the turn-initial particle "a"), the largest set of combined turn-beginning elements involving "demo" in the database. This study reveals that "demo"-prefacing fundamentally serves to proffer qualification upon implied affirmation. When used with "a," "demo" registers question recipients' implied acknowledgment of the legitimacy of the question's presupposition while projecting disaffirmation of the inquired proposition.