PURPOSE: To optimize the axial weight ratio between a single and double shafts in a suspension device such as a track crane whose foremost and rearmost shafts are single wheel steering axes by specifying the 3-beam arm ratio of an equilibrium beam for supporting the shafts.

CONSTITUTION: In a large vehicle provided with adjacent four shafts 8, 9, 7, and 10, foremost or rearmost shafts of which are single wheel type steering axes 7 and 10, and others are double wheel type non-steering axes 8 and 9, the axial weight ratio of each shaft is distributed to 0.4W0.7:1:1:0.4W0.7 by setting the arm ratio of three pairs of beams 15, 17, and 19 that comprise an equilibrium beam for supporting the shafts under the specific conditions. In addition, the shafts 8, 9, 7, and 10 are mounted axially movably to the equilibrium beam 15, 17, and 19 so that large swing displacement with lateral symmetry and asymmetry of the shafts 8, 9, 7, and 10 may be fully allowed. Furthermore, a tire is prevented from falling on an abnormally low road surface by limiting the downward swing displacement of the shafts 8, 9, 7, and 10 by means of a stopper 41 and increasing the upward swing displacement to the extent of the above limitation.