COUNTERWEIGHT

PURPOSE: To prevent the occurrence of welding distortion on the surface of a counterweight rear plate, when a reinforcement plate and a mount member are fixed to a counterweight internally in a lengthwise direction. CONSTITUTION: A counterweight 21 is constructed to have a hollow structure made of a front plate 22, a rear plate 23, a side plate 24, an upper plate 25 with a pair of welded screw members 17, a lower plate, and a pair of mount members 27 with screw members 14 welded to upper surface. In addition, the counterweight 21 is internally fitted with a pair of reinforcement plates 29 extended in a lengthwise direction. The mount members 29 are respectively welded to the lower plate 26 and the front plate 22. Also, the reinforcement plates 29 have the lower ends welded to the screw members 14 and the mount members 27, the upper ends to the upper plate 25 via the screw members 17 and the front ends to the front plate 22, respectively. At the same time, the rear ends of the mount members 27 and the reinforcement plates 29 are separated from the rear plate 23. According to this construction, welding distortion is prevented from occurring on the surface of the front plate 22, with the strength of the reinforcement plate 29 properly maintained, and accuracy required for appearance is enhanced.