Connecting device for lorry-mounted crane

The utility model discloses a connecting device for a lorry-mounted crane, which comprises a square-head bolt, a nut and a square-head positioning device; the square-head bolt goes through corresponding through holes on the lorry-mounted crane and a frame; the nut is jointed with the threaded part of the square-head bolt; and the square-head positioning device is arranged on the lorry-mounted crane for positioning the square head of the square-head bolt so as to prevent the square head from rotating. Therefore, when the lorry-mounted crane is connected to the frame, the square head of the square-head bolt is positioned by the square-head positioning device but does not rotate with the tightening torque applied on the threaded part, so that the reverse tightening torque does not need to be applied on the square head. Consequently, quite good assembly technology is provided.