PURPOSE: To raise the effiiency of operations by providing the second stepping pedal serving to keep the relief pressure of a relief valve maximum to a modulation mechanism.

CONSTITUTION: On the way of a fluid pressure supply path from a fluid pressure pump 19 to a control valve 22 for change of gear, a relief valve 20 to alter the pressure of change gear operation and a modulation mechanism 21 to gradually increase set relief pressure of the relief valve 20 as the advancing operation proceeds are provided. The first stepping pedal 30 taking charge of the opening and closing operations of the valve is connected to the relief valve 20. The second stepping pedal 31 serving to keep the relief pressure of the relief valve 20 maximum is provided to the modulation mechanism 21. Since the rash operation of a bucket by abrupt advancing during the operation period of the shovel loader can be performed satisfactorily, the efficiency of operations can be raised.