Education based on synesthesia has been used to be applied for several years. Especially, We focused on the Coloured-hearing Synesthesia for music education for children who have difficulty in practicing pitch by using the serious game based on Coloured-hearing theory. Also, smart platform is flexible for several sort of video games so we expect good accessibility for children. For proving the effectiveness for education by using this technology and theory, we design the serious game for music called “Bunny’s Cave” based on Coloured-hearing theory and conduct the usability test aimed at 3rd grade student in elementary school.