PURPOSE: To measure a position and azimuth with good accuracy by loading a rate gyro and rotary encoder on board the travelling robot travelling autonomously inside a plane face and by removing the effect of a disturbance.

CONSTITUTION: The rotary encoder 8, 19 directly fitted to a wheel shaft measures the rotary pulse of wheels 7, 18 and the output pulse thereof is counted by pulse counter circuit 9, 20. The position of a robot is found from the extent of movement variation of the right and left wheels 7, 18 with said counted number and the wheel diameter. A rate gyro 10 outputs the angular speed of the robot, LPF11 removes the vibration of the gyro 10 itself and the vibrations from driving motors 5, 16 and passes through nearly the direct current component only. The azimuth of the robot is found with the time integration of the angular speed signal of the gyro 10 thereof. The gyro 10 is provided inside a thermostatic chamber since it is easily effected by the atmosphere. The self position and azimuth of a self travelling robot can thus be measured with good accuracy.