We have proposed a system of real-time measurement and visualization for three-dimensional (3D) sound field by using mixed reality (MR) device. MR device enables effective visualization with depth perception using the 3D computer graphics (3DCGs) superimposed on the real world. Our system can superimpose 3D sound intensity data on the measurement points in the see-through head mounted display (STHMD). It helps us not only to understand the sound field but also to design it, to detect the source of noise, etc. Sound intensities are measured by freely and slowly scanning the sound field with a handy 4-ch microphone array. However, the measurement results of sound intensity would be affected by assuming a moving microphone array as fixed one. In this paper, we investigate the effect of microphone movement on sound intensity. To clarify the maximum of handy microphone speed to be assumed, microphone speeds were measured in measurement of sound field by using our proposed MR visualization system. Then, simulation experiments in a plane wave and a spherical wave were conducted to compare the sound intensities by fixed and moving microphone array at different speeds.