lower than the rear side portion with respect to a horizontal plane the rod propelling device 3 is provided with a frame 4 which may be called hereunder as frame structure 4 a cradle 5 reciprocally movable along the longitudinal direction of the frame 4 a motor 6 for rotating a rod mounted to the cradle 5 an anchor fixing portion 7 mounted to a front lower portion of the frame 4 a rod wrench 8 mounted to a front upper portion of the frame 4 a rod damper 9 and a rod propelling motor 10 disposed to a rear portion of the frame 4 thus the rod propelling device 3 is provided with a mechanism for reciprocally moving the cradle 5 this mechanism for reciprocally moving the cradle 5 is provided with a driving drive sprocket 11 mounted to a rear portion of the frame 4 a driven sprocket 12 mounted to a front portion of the frame and a chain stretched around these driving and driven sprockets 11 and 12 the driving sprocket 11 is rotated in a reversible manner by means of rod propelling motor 10 and the chain 13 is connected to the cradle 5 according to such structure when the driving sprocket 11 is normally rotated by the rod propelling motor 10 the cradle 5 is moved forward and then when rotated reversibly the cradle 5 is moved rearward.