QZSS (quasi-zenith satellite system) is a Japanese satellite navigation program with a regional service coverage planned to be launched in 2009. In order to broadcast radiosignals from high elevation angle into urban canyons, the QZS (quasi-zenith satellite) will be launched into a 24-hour elliptic orbit inclined 45 degrees on which a satellite is kept within a certain range of geographic longitude and stays above Japan at least 8 hours everyday. QZSS will offer both supplement and augmentation signals in order to offer the maximum benefit to users. QZSS will broadcast GPS augmentation messages on the GPS L1 frequency. For this purpose L1-SAIF (submeterclass augmentation with integrity function) signal has been developed based on SBAS standard because both of them offer similar function to the almost same service area. The target of positioning accuracy with augmentation was set as 1 meter for horizontal. QZSS will also provide the integrity function necessary for safety of mobile users. L1-SAIF augmentation messages are being designed to be upper compatible with SBAS messages; The extended messages are designed to enhance the performance of augmentation system. Performance analysis of the L1-SAIF augmentation message has been conducted using the prototype SBAS software developed by ENRI. This prototype has capability to simulate L1-SAIF MCS and to generate augmentation message stream which could be used to evaluate the actual position accuracy at any user location. According to the result the target accuracy is likely achievable. The prototype has been operating continuously since April 2006 for long-term test, and so far it is stable and any troubles have never been detected. Furthermore, most recently realtime message generator has been developed and tested with realtime data connection from GEONET observation sites. The prototype is functional and stable even in realtime mode.