In this paper, we design a computer game that helps improve children' s music aptitude according to their levels. The game is called "Music Space" and is designed to develop ability for rhythm, melody, and harmony. The game is designed for children under age 9. Music Space is targeted to improving children's hearing ability. This game will help children improve their music ability by playing and enjoying games. It also enables personalized learning according to children ' s ability. In the game, children are supposed to hear music several times, and to do practice of reading notes. The rhythm game consists of beat and rhythm pattern games. The beat game consists of games for regular beat, weak and strong beat, and ostinato. The rhythm pattern game has to do with distinguishing and playing rhythm patterns, and identifying and reading the notes for rhythm patterns. The melody game consists of distinguishing low and high notes, distinguishing melody patterns, identifying notes for melody patterns, and completing a melody. The harmony game consists of distinguishing harmonic and inharmonic sounds, finding harmonies corresponding to given harmonies, and playing harmonies. At the moment, the game is only designed, and not yet implemented. We need to implement the game and evaluate its effectiveness by having children play the game. But because this kind of study is new in the field of music education, we think it worthwhile to publish the design of the game and get some feedback.