To bring a working deck near to the face of a slope as the object of working while ensuring the elevation of a drill guide arm in a high-place workbench device for slope protection works with the working deck installed at the front end section of an expansion boom mounted on a car in a freely slewing-derricking driving manner in a freely horizontally slewing driving manner through a posture maintaining member and a percussion device for drilling the face of the slope set up on the working deck.

In a working deck 6, a forward opened outside-opened notch is formed at a central section on the front side of an approximately rectangular floor-face shaped floor face 6a, and the working deck is formed in one 6 having a recessed floor face shape in a plan view as a whole. The base 7a of a percussion device 7 is arranged to the inward section of the outside-opened notch, and the elevation of a drill guide arm 7b can be ensured through the outside- opened notch 6b.