the control input detection means 17 and a mode change switch 19 to be mentioned later and outputs a control command to the first electromagnetic proportional control valve 12 and the second electromagnetic proportional control valves 14u and 14d in accordance with these input signals the structure of the control section 18 is described below by referring to fig3 in fig3 reference character 22 denotes a signal conversion unit the signal conversion unit 22 is set so as to input a signal from the control input detection means 17 and convert the magnitude of the input signal that is the magnitude of the control input of the operating lever 16 according to a plurality of preset logical functions before outputting the resultant output signal specifically in the case of this embodiment seven types of logical functions are set as shown by 1 to 7 in fig4 v that is the conversion unit 22 is set so as to output a converted input signal by increasing the input signal in magnitude according to one of the logical functions 1 to 3 keeping the output signal directly proportional to the input signal according to the logical function 4 or decreasing the input signal in magnitude according to one of the logical functions 5 to 7 a logical function to be adopted out of the above described logical functions can be selected by the mode change switch 19 moreover the signal output from the signal conversion unit 22 is input to a pump rate limiter 23 and a valve.