bucket 4 respectively these arm angle detector 60 and bucket angle detector 61 which can be for example rotary potentiometers respectively detect the arm angle u03b2 and the bucket angle u03b3 and then output the corresponding arm angle signal e u03b2 and bucket angle signal e u03b3 levers 11 to 15 respectively send out lever control signals ea to ef corresponding to the operation angle of each lever and at the same time in case of the levers 13 14 and 15 in particular send out signals vc vd and vf which indicate that the lever is being operated that is the lever is not in the neutral position a manual auto changeover switch 16 in a control device 10 is for selecting the control mode of the arm cylinder 6 and the bucket cylinder 7 from manual to automatic and vice versa and sends out signal 34 0 34 for the manual mode and 34 1 34 for the automatic mode a control circuit 20 sends out when receiving the boom lever control signal ec the bottom lever control signal ed and the rotation lever control signal ef together with the boom lever operation signal vc the bottom lever operation signal vd and the rotation lever operation signal vf an automatic control command signal e c which determines control mode in the operation of the arm 3 and the bucket 4 when bringing the bucket 4 into the original excavation posture after dumping the excavated soil after the bucket 4 scooped up the excavated soil raise the bucket 4 and rotate the rotation body 1a up to the dumping place when the dumping place is located in the right.