Messages to notify users of application states (hereafter notification messages) such as error, warning, confirmation, and information messages are often used in user interfaces. Generally, error messages are the most critical, while information messages are the least. However, the types of notification messages are determined in terms of what the application can or cannot process successfully instead of what the users feel are the most critical issues. Currently, human centered design (HCD) focuses on users’ aspects. HCD emphasizes users in application development to realize a high usability. Thus, we propose a strategy to realize notification messages considering HCD. Concretely, we analyze existing notification messages in terms of the criticality level by users and define new types of notification messages. In addition, we develop guidelines to implement notification messages effectively. Our strategy allows users to be appropriately notified based on the criticality.