This paper proposes practical Demand Responsive Transit (DRT) system with a new reservation processing called “Insured Announced Time Reservation System (IATRS)”. DRT service has been expected as an alternative mode in public transportation which aims to improve mobility in a city. However, it was initially impractical because the routing system cannot assure reserved passengers that vehicles will arrive at the passengers’ destination by the announced arrival time. The developed IATRS for this new DRT service intends to ensure the announced arrival time by employing a slack time variable and a new proposed algorithm. The program composes of vehicle-choosing and routing algorithms. The vehicle-choosing algorithm decides which vehicle will accept the new reservation, while the routing algorithm designs the new route and schedule for the vehicle chosen to serve the new reservation. The system calculates and updates the route of the vehicle and returns the pick-up time to the customers immediately during reservation. Moreover, the vehicle will not delay the announced arrival time of passengers who have reserved already even if new passengers are added and the schedule of the vehicle is updated. In order to validate the proposed DRT service, one experiment was conducted in Kashiwa City, Japan in 2008. In the experiment in Kashiwa City, which is recognized as a commuters’ town of Tokyo metropolitan area, 3851 passengers used the about five DRT vehicles in 40 days (480 hours). It was shown that the characteristics of this system worked very well, and more than 44.7 percent of passengers were satisfied with the DRT service because they can make a reservation via personal computers and they were able to specify dependable arrival time or pick-up time. And 36.1 percent of passengers answered that their chances of going out increased by the introduction of DRT service. The result of Willingness To Pay (WTP) analysis is more than twice of fixed bus (353 yen / ride). In conclusion, the result of experiment showed the developed DRT service is a practical alternative mode for public transportation.