Speech can affect the behavior of the listener. Our previous study showed that the stimulus-organism-response theory using emotional states can explain a person's willingness to buy from advertising speech. In addition, there have been reports of the influence of voice quality in speech, which differs from other advertising stimuli, but few studies have been done on willingness to buy. In this study, we conducted an experiment to determine whether voice quality affects the willingness to buy from advertising speech. Participants listened to advertising speech and rated their willingness to buy the products advertised and their own emotions and voice quality. We found that a model constructed using voice quality as a mediator can better explain the willingness to buy from advertising speech. These results could help train salespeople in advertising speech.