EXCAVATOR

PURPOSE:To widen the area to be excavated by widening the arm bending angle made by the upper boom and the bucket arm when the excavating angle between booms is small, and lessening the bending angle when the excavating angle is large. CONSTITUTION:When excavating by a bucket, an extensible cylinder 7 is constricted to lessen the excavating angle alpha between booms constituted by the lower boom 1 and the upper boom 4 to close the bearing point 8b of the arm cylinder to the bearing point of the booms 1b to bring about the distance (a) and further to widen the arm bending angle beta. When turning the machine body or the excavator in a narrow space, the cylinder 7 is extended to widen the excavating angle alpha between the booms and lessen the arm bending angle beta.