The present invention relates to a self-propelled working robot, including a first distance sensor 4a and a second distance sensor 4b (4c) for measuring the distance to an obstacle W in front of the robot. The robot includes first determination means for comparing a first measured distance Dc to the obstacle obtained by the first distance sensor 4a with a predetermined first threshold value to determine the proximity to the obstacle W, second determination means for comparing a second measured distance Dr (D.sub.L) to the obstacle W obtained by the second distance sensor 4b (4c) with a predetermined second threshold value to determine the proximity to the obstacle, and changing means for changing the first or second threshold value based on information regarding an inclination angle of the obstacle W obtained from the first and second measured distances.