To solve the problem of danger attributable to the change of engine speed and discharge oil quantity of a hydraulic pump caused by rotationally operating a grip throttle unconsciously during turning operation in a conventional grip control device.

Pilot lines 9a and 9b of a turning lever 1 are provided with a turning pressure switches 8a and 8b. When the turning lever 1 is operated, the contact of either one of the pressure switches 8a and 8b is closed by the operating pressure to output a turning operation signal gs. During the output of the turning operation signal gs, a computer 5 invalidates a rotating position signal ps outputted anew from a potentiometer 4 by the rotating operation of a grip throttle 2 and controls a throttle motor 6 and a solenoid proportional valve 7 on the basis of a rotating position signal outputted from the potentiometer 4 before the output of the turning operation signal gs. The engine speed and the discharge oil quantity of a hydraulic pump are not therefore changed during turning operation.