PURPOSE: To provide the underwater running machine which is automatically run while avoiding collision with obstacles in water where obstacles having three-dimensional shapes exist.

CONSTITUTION: The underwater running machine which is automatically run in water by automatic steering of a running wheel part 2 is provided with at least one ultrasonic sensor 4 which transmits an ultrasonic wave to the periphery or the running machine and detects the reflected ultrasonic wave, a scanning part 6 which scans this ultrasonic sensor 4 in vertical and horizontal directions, and a control part 5 which recognizes the peripheral condition of the running machine from detection data obtained from the ultrasonic sensor 4 and the scanning part 6 as three-dimensional information and controls the running wheel part based on this information. Obstacles around this machine are three-dimensionally recognized, and the running machine is automatically run while avoiding the obstacles.