Visualizing sound fields is important to understand them intuitively. Recently, sound field visualization using a parallel phase-shifting interferometer (PPSI) has been proposed. This optical method can observe a sound field instantaneously and quantitatively without placing any object inside the field. Thus, sound fields difficult for the ordinary instruments to measure can be investigated by PPSI such as the fields inside a small cavity or air flow. After a measurement, the observed data must be analyzed to obtain meaningful information in terms of acoustics. However, such analysis has not been studied much as PPSI itself is a newly developed method. In this paper, we estimate sound intensity from the data captured by PPSI. The number of the observation points of our PPSI system is up to 262,144, where the interval between the adjacent points is 0.22 mm. Therefore, sound intensity can be estimated densely at quite a lot of points. The accuracy of estimated sound intensity is investigated through numerical experiments, and then real data observed by PPSI are analyzed for visualizing the sound intensity.