PURPOSE: To provide a device to examine the bearing force of the ground part where the grounding plate 4 of an outrigger jack 1 is in contact, in advance prior to the crane works or high place operations.

CONSTITUTION: An outrigger jack concerned 1 consists of a guide part 2 dangling on the vehicle A side and an expansion/contraction part 3 which is equipped with a grounding plate 4 at the bottom and guided with possibility of being expanded and contracted in the direction downward in the guide part 2, and the bearing force examining device concerned is to be mounted on the outrigger jack 1 and to sense the bearing force of the ground part where the grounding plate 4 is in contact. The grounding plate 4 is equipped with a penetration sensing tool 6 so that it is movable between the protrusive position at the undersurface of the plate 4 and the non-protrusive position, while the guide part 2 has a penetration sensing tool pressing means 9 furnished with an expansion/contraction rod 9a, whose bottom at the time of elongation is detained with the penetration sensing tool 6 to push it in the direction of protruding.