To simplify a connecting structure by a pin of a cylinder for slewing an arm and a cylinder stay in the front attachment of a hydraulic excavator for a side ditch while lightening bending force and shearing force applied to the pin, and to improve safety in the case of excavation while reducing the quantity of the lifting of the rear end of the cylinder for slewing the arm in the same manner as conventional devices.

A boss 34, to which a pinhole 34a is formed in the orthogonal direction to the axis of a cylinder 30, is installed integrally to an intermediate section on the upper side of the cylinder 30 for slewing an arm by welding. One through-pin 35 is inserted into the pinhole 11a of a cylinder stay 11 and the pinhole 34a of the boss 34, and the cylinder 30 for slewing the arm is connected to the cylinder stay 11.