A bubble generation method that uses a slit elastic tube and an acoustic pressure wave in the gas phase can produce single bubbles of various sizes. In the method, the bubble size greatly depends on the tube length and the boundary condition of the tube end. In this study, we investigated the effects of acoustic pressure waveforms on the bubble generation. We changed the tube length and the boundary condition of the tube end and measured the waveform using the electret condenser microphone (ECM) and the generated bubble diameter. The time length that the positive pressure was maintained on the waveform depends on the tube length and the boundary condition. The diameter of the generated bubble also changed with the time length. We demonstrated that this phenomenon was caused by the change of the phase of reflected wave at the tube end by using FDTD simulation.