Spin waves propagating in a waveguide have eigenmodes depending on the standing waves formed in the perpendicular direction. Although it is functional to excite high order spin wave modes, it has been difficult to excite a high order spin wave mode selectively. In this work, we numerically investigated spin wave excitation in a T-shaped magnetic device, and we consequently found that even high order spin wave modes are selectively excited by optimizing the frequency and the dimension of the T-shaped structure.