Present study investigated the effects of the geometry changes of the waveriders on aerodynamic characteristics by using the numerical simulations. This study introduces the two types of waveriders which have simplified lower surface; one is composed from two planes (Two-flat waverider) and the other is from one plane (Flat waverider). The ideal waverider, which has the ideal lower surface shape, is designed from the conical flow field for the angle of attack of 0 degree and Mach number of 4.0. The numerical simulations for three waveriders each shape are performed in inviscid and viscous cases. The numerical results for ideal waverider show that the rate of decrease of L/D between viscous and inviscid cases is the largest in the three waveriders. Therefore the ideal waverider designed by the inviscid assumption is affected by the viscous effect. The L/D of flat waverider decreases at the positive angle of attack because its drag coefficients increase. The longitudinal stability of three waveriders is not obtained as the center of gravity is placed at 70% of fuselage length.