A high-precision position and orientation localization system for an indoor mobile robot, which utilizes non-directional ultrasonic sensors and radio frequency wireless communication, is proposed in this paper. The transit times of the ultrasonic pulses from a transmitter attached to the robot to four receivers located on the ceiling are measured, and the transmitter's position is obtained by a simple triangulation principle. An electric spark, which works as a non-directional point sound source, is adopted as a transmitter. Since the transit times are obtained by a subsystem set on the ceiling, a measurement demand signal and transit times data are sent via wireless communication between the robot and the ceiling. A position measuring method proposed in this paper estimates in real time both the delay time of wireless communication caused by the modulation process and the sound velocity in the measured space. Static position accuracy of this system is experimentally inspected. It is proved that the accuracy is several mm and fairy good compared with other systems using image processing, etc. The developed system is mounted to a mobile robot and practical dynamic position and orientation accuracy is also inspected.