A construction machine where an operating load is transferred to a location having good rigidity, thereby ensuring the strength of a vehicle body and increasing the load-withstanding strength in relation to running loads. The frame of the lower traveling body of the construction machine comprising a hollow center frame having an upper plate with an attachment ring, a lower plate, and side plates that surrounding sides of the frame and that jut out from the attachment ring, and reinforcing ribs which connect the upper plate to the lower plate in the interior of the center frame beneath the attachment ring.