Abstract: In a hydraulic dredger/excavator wherein it is desired to guide the bucket parallel to itself there is provided a control apparatus for positively controlling the necessary changes of angle between the dipper boom (4) and the bucket (5) in dependence on the change of the angle between the boom (2) and the dipper boom (4). The control apparatus has a cam disc (11) on the end of the boom (2) against which the piston rod (13) of a first control cylinder (12) arranged on the dipper boom engages under the effect of a spring (15). Both cylinder spaces or chambers of the double-acting first control cylinder (12) are connected with the corresponding cylinder spaces or chambers of a double-acting second control cylinder (16) via lines or ducts (17, 18). The second control cylinder is arranged to be parallel with the operating cylinder (10) that serves for changing the angle between the dipper boom (4) and the bucket (5).