Recently attention deficit of children has caused various social problems. Those children who has symptoms like ADHD (Attention Deficit/Hyperactivity Disorder) has to be provided with methods which can enhance their attention level in a child-friendly way such as 3D games. This paper shows a research on how to measure the level of attention for attention deficit children using their favorite 3D games. Firstly, we speculated on the methods about attention measurement used in the medical area. And then we searched measurement variables which can effectively evaluate the level of attention during a game play time. Secondly, we have conducted experiment whether there exists difference about the value of the measurement variables between the two groups, normal children group and attention deficit children group. Those variables are omission error, commission error, average response time, and standard deviation of response time. Though our experiment has only been limited to visual attention level, four measurement variables revealed mutual differences.