When using software, various notification messages are displayed in response to users' operations. Although each notification message has its own importance level, users often do not perceive the importance level. For example, they just proceed with an operation without reading the content or they do not notice the notification itself. Meanwhile, sound is a common resource used to convey the importance of a situation and is often employed to make users aware of notification messages. Thus, it is effective to represent the importance of the notification message by sound. However, sound importance depends on the user. This paper proposes a determination method of notification sounds by evaluating the importance level of sounds by users. Then sounds are assigned to notification messages according to users' input.