To easily recognize where a connecting relation of an operation lever device and a directional change-over device is on a hydraulic system furnished with an operation type change-over valve.

An operation type change-over valve 2 to change a connecting relation of operation lever devices 11, 12 and directional change-over valves 31-34 and to change operation types of the operation lever devices 11, 12 is provided, a connecting relation of a pump port 2a, a tank port 2b and output ports 2c and 2d is provided on this operation type change-over valve 2, a different pressure signal transmitted at each of change-over positions is detected by pressure switches 51, 52, and it is input to a controller 4 as an electric signal. The controller 4 judges the change-over position of the operation type change- over valve 2 by combination of on and off of the electric signal and displays a judged result on a position display device 6 provided in a driver's cabin.