This study examines methods for executing high-speed three-axis attitude maneuvers for spacecraft with flexible structures. To apply the design methodology of feedforward control input for single-axis attitude maneuvers to three-axis maneuvers, we realized three-dimensional rotation as a single-axis rotation around the Euler axis. First, we expressed the equations of motion of the spacecraft in a coordinate system with the Euler axis as the single axis. Next, we derived the equations of motion for the global modes. Using these equations, we demonstrated that the control input is applied to the single axis around the Euler axis, achieving three-axis attitude maneuvers. Numerical simulations were conducted using two types of feedforward control inputs: step-type and continuous-type. The results indicate that the continuous-type control input excites almost no oscillatory modes and achieves minimal attitude error. On the other hand, the step-type control input requires less control torque compared to the continuous-type for the same maneuver duration. By adopting a two-degree-of-freedom system that simultaneously uses feedforward and feedback control, we demonstrated robustness even in the presence of variations in vibration frequencies and damping.