Conventional rockets are faced with several problems such as high launching cost. Therefore, in Japan, a reusable vertical-takeoff-and-vertical-landing (VTVL) rocket vehicle is being developed. This vehicle utilizes nose entry as the return flight system including the attitude change (turnover) due to aerodynamic forces. To safely achieve turnover, it is necessary to reduce the difference between the maximum value and minimum value of C_m (i.e., pitching-moment coefficient). In this study, a delta-wing with vortex flaps (developed for the aircraft industry) is attached to the aft of the vehicle with the expectation of improving the C_m characteristics during the turnover process. Consequently, when the flap deflection angle is 0°, the nose-up C_m can be reduced at forward angles (i.e., AOA 0° - 90°) because vortices generated by the fins result in a nose-down C_m and cancel the nose-up C_m. Moreover, when the flap deflection angle is -30°, the nose-down C_m is enhanced at the backward angles (i.e., AOA 90° - 180°) because the flaps reduce the vortices generated by fins. Hence, setting the flap deflection angle at 0° for the forward angles and -30° for the backward angles reduced the difference between the maximum and minimum values of C_m (i.e., 12% smaller than a conventional model).