To improve arrangement freedom of a second steering wheel, to set its steering angle larger than a steering angle of a first steering wheel and to reduce a turning radius by furnishing the second steering wheel the steering angle of which is larger than that of the first steering wheel in the rear of a rear side outrigger.

A walking crane 1 has an upper part revolving superstructure 3 on a main frame 2 free to revolve and is furnished with a front side outrigger 4 on a front part of the main frame 2 and a rear side outrigger 5 on a rear part of it respectively. Additionally, a front wheel 7 and a rear wheel 8 as a first steering wheel are arranged on the left and right outsides of the main frame 2 between the front side outrigger 4 and the rear side outrigger 5. In this case, a comparatively narrow sub frame 6 is fastened on the rear side of the main frame 2, and a second steering wheel 9 is arranged on the left and right outsides of this sub frame 6. Thereafter, in this case, when the maximum steering angle of the front and rear wheels 7, 8 is specified as θ1M, the maximum steering angle θ2M of the second steering wheel 9 is set larger than θ1M.