Apparatus for controlling a boom-holding on travelling of excavator

A boom-holding control device brings an excavator boom into a holding condition or a release condition. The device includes a boom-holding valve (15) provided on a fluid pressure line (14) for preventing boom deadweight-caused drainage of a hydraulic flow from a boom cylinder (13) to thereby keep a boom in a holding condition, a boom release valve (19) for releasing the boom from the holding condition in response to at least one of a boom-down pilot signal pressure (P dn ) supplied from a boom cylinder remote control valve (20) and a travel signal pressure fed from a travel control operator-interface device and a solenoid-actuated changeover valve (25) provided on a travel signal line (24) for selectively opening and blocking off the travel signal line (24). The changeover valve (25) is normally kept in a closing position and will be shifted to an opening position at the time of simultaneous activation of a travel selection switch (26) and a boom release switch (28).