PURPOSE: To provide precise machining with a machine tool for a long and heavy work, by using a balancer for eliminating a gravity applied on the work due to the weight of the machine tool by which the work is held.

CONSTITUTION: A cylinder 11 and ram 14 of a drilling machine are energized and upper and lower blocks 15, 13 are separated from each other, so that a work 7 can be fed laterally. Being positioned on the lateral side of the work 7, the drilling machine is moved vertically by means of a balancer 18 in order not to interfere with each other when both blocks 15, 13 are moved toward the work 7. The balancer 18 is then shifted horizontally along an arm 21 for positioning, so that the center of a straight groove on the upper block 15 and the center of a V-groove on the lower block 13 pass the center line of the work 7. Both blocks 15, 13 are shifted by energizing the ram 14 and cylinder 11, and the work 7 is held between both blocks to support the drilling machine. At this moment, the weight of the drilling machine is eliminated by the balancer 18, having no effect on the work 7 itself.