Sound field visalization is an effective technique to understand spatial sound information. For example, acoustical holography, optical methods, and beamforming have been proposed and studied. In recent years, mixed reality (MR) technology has advanced rapidly and is now more familiar. Many sensors, display devices, and ICT technologies have been implemented in MR equipment, which enable interactions between real and virtual worlds. In this paper, we propose an MR display system that displays the results obtained by the beamforming method. The system consists of a 16ch microphone array a real-time sound field visualization system and an optical see-through head-mounted display (OST-HMD). The real-time sound field visualization system analyzes sound signals recorded by the 16ch microphone array using the beamforming method. Processed sound pressure data are sent to the OST-HMD using a transmission control protocol (TCP), and a colormap is projected on the real world. The settings properties of a real-time sound field visualization system can be changed by using a virtual user interface (VI) and TCP. In addition, multiple users can experience the system by sharing sound pressures and settings property data. Using this system, users wearing an OST-HMD can observe the sound field information intuitvely.