To facilitate improvements in the speech of patients with tongue resection or tongue movement disorders, palatal augmentation prosthesis (PAP) was proposed and its efficacy has been widely recognized. However, patients cannot enjoy conversation during meals, because they have to put a wearable device in their mouth. Therefore, we propose another approach to improve speech quality by using digital signal processing, particularly a voice conversion algorithm. Voice conversion is a technique that changes a speaker’s individuality, i.e., speech uttered by speaker A is changed to sound as if another speaker B had uttered it. Our approach does not require that an individual wear any special equipment, which results in more natural opportunities for speech communication.