Many schemes for indoor positioning have been investigated so far. The shortcoming of the system using wireless LAN is positioning accuracy and the system composed with RFID needs dense placement of RFID tags in the floor. We propose a platform which is composed with positioning by inertia sensor embedded in a smartphone and ultrasonic sensor positioning system whose positioning error is within 10cm. This platform can easily correspond to accuracy requirement and positioning range. This report describes a basic configuration of proposed platform and required element technologies. The new system configuration for the ultrasonic positioning system and basic experimental results for inertia positioning have been shown to prove the validity of the proposed system. Detection tests of walking steps and cornering were carried out for inertia positioning. Steps detection accuracy about 98% and nearly 100% accuracy for cornering by hand carrying were clarified by experiments. It was verified that requires positioning accuracy can be realized by combining ultrasonic and inertia positioning method.