In a nuclear power plant, one of the important issues is an evaluation of the safety of a system when an earthquake occurs. However, there is little knowledge how coolant (single and two-phase flow) response when large earthquake acceleration is added. The aim of this study is to clarify the influence of vibration on bubbly flow behavior in structures by using state-of-the-art experimental and numerical techniques. In order to investigate the influence of vibration on a bubbly flow behavior in structures, we visualized a bubbly flow in the pipeline on which a sinusoidal wave was applied. In the test section, the bubbly flow was produced by injecting nitrogen gas into the liquid flow through the horizontal circular pipe. In order to vibrate the test section, the test section was installed on an oscillating table. A high-speed video camera was fixed on the oscillating table to ignore the relative velocity between the camera and the test section. In this paper, based on observed images, bubble velocity was evaluated. The frequency and acceleration of vibration added from the oscillating table was from 1 Hz to 20 Hz and 0.4 G (=3.92 m/s^2) at each frequency, respectively. Liquid pressure was also measured at upstream and downstream of the test section. It was observed that the pressure gradient amplitude increased with the increase of the frequency of the table. Furthermore, it was confirmed that the bubble velocity amplitude also increases with the increase of the frequency of the table. It was concluded that the bubble motion was strongly affected by the pressure difference. In addition, to consider detailed effects of pressure gradient on bubble motion, numerical simulation of two-phase flow in horizontal pipe with vibration was performed by a detailed two-phase flow simulation code with an advanced interface tracking method: TPFIT.