This research aims at a comprehensive understanding, taking individual differences into account, of how the loss of skills acquired in a music game is influenced by factors such as the speed at which skills are learned and previous experience of music games. Using Sparebeat, an online music game, we conducted an experiment in which seven participants were each assigned a piece of music which they practiced every day, their scores being recorded, until they were determined to have reached a certain skill level. Then, they entered a ‘non-training phase’ in which they did not practice for one week, before playing their assigned piece again and having their score recorded. The state of skill loss was measured by repeatedly recording participants’ scores at one-week intervals and comparing these to the scores at the end of the training phase. By analyzing the changes in score in the phases of skill acquisition and skill forgetting, we discovered two forgetting patterns, namely, maintenance of score and decrease in score. In addition, to study the influence of difficulty level on skill loss, we also analyzed the scores participants obtained on two pieces of music of different difficulty levels from their assigned pieces. Furthermore, we investigated participants’ previous experience regarding playing music and music games. As a result, we found that participants with music game experience tended to maintain their scores, while the scores of participants with musical experience tended to decrease. This suggests the possibility that having musical experience accelerates skill loss.