This paper presents the development of pseudo 3D visualization system of organs using 2D ultrasound images for a new medical instrument. The new instrument consists of an ultrasonic endoscope and an electro-magnetic measurement sensor. The pseudo 3D volume is reconstructed by superimposing ultrasound images captured by the ultrasonic endoscope. So the new instrument shows not only the surface of organs, but also the 3D volume of inside of organs. However, it was reported that the ultrasound probe influenced the accuracy of the sensors, so it is necessary to investigate the influence of the ultrasound endoscope to the sensor. In this paper, we propose a 3D volume reconstruction system using 2D ultrasound images, and show experimental results of accuracy measurement experiments of two kinds of electro-magnetic measurement sensors and 3D visualization with actual ultrasound images.