To provide a travelable working machine which causes no damage both to a working unit and an obstacle, when the working unit collides to the obstacle and escapes from the obstacle.

When the machine body 2 travels forward and the working unit 5 collides to the obstacle T, the working unit 5 is relatively pushed b the obstacle T whereby the working unit 5 escapes and rocks backward in the advancing direction of the machine body 2. At this time, even when the machine body 2 is allowed to go forward, a plurality of the guide rollers 28, 28,... equipped in series along the front edge 32 of the working unit rotate as they come into contact with the obstacle T and the resultant friction between the working unit and the obstacle becomes very small. Thus, both of the working unit 5 and the obstacle are never damaged.