Acquiring one's own form is an important technique for excelling in any competitive sport. Most basketball players spend a significant amount of time in acquiring the ideal form in order to improve their basketball skills. Although basketball is one of the most popular sports in the world, there are only few devices that aid in improving a player's skills. In the research involving the development of a skill-support device for basketball, it is important to learn the ideal form to acquire a physical posture of set-form. Therefore, we developed a device for reforming the set-form using auditory biofeedback. The proposed device measures the shoulder angle of a player in real time (50 Hz) and generates a sound on the basis of the measured angle to inform the ideal posture. If the set-form posture is not ideal, the device uses this sound to inform the player that they must modify their posture. The player then changes their shoulder angle and if the posture becomes ideal, the device mutes the sound. Several seconds after the sound stops, the device indicates the player to shoot. According to our study for testing the efficacy of this device, the BF-training group obtained 20% higher success rate than the control group. Moreover, the BF-training group had a more stable form than the control one.