Four quasi-zenith satellites (QZS) in Japan was completed at 10th October 2017. As a result, QZS system can be able to observe in 24 hours. Since QZS has a special orbit, it is possible to stay at the zenith of Japan for a long time. In this paper, we describe QZS system and relationship between QZS and other GNSS. QZS has two Japanese special service which is called centimeter and sub-meter grade. Each type is adopted many service for traffic, railroad, civil engineering, and maps. The application using QZS contributes to security, safety and comfortable life for safety confirmation, navigation, logistics, construction and agriculture.