A hydraulic control device, comprising: a boom attached to a base machine to be operable to be raised and lowered by pivotal movement around a boom foot pin; an arm attached to a distal end of the boom to be operable to be pushed and pulled; a boom cylinder for raising and lowering the boom; an arm cylinder for pushing and pulling the arm; a first hydraulic pump and a second hydraulic pump as a hydraulic source of the boom cylinder and of the arm cylinder; a boom cylinder circuit for connecting the first hydraulic pump and the boom cylinder; an arm cylinder circuit for connecting the second hydraulic pump and the arm cylinder; a boom control valve disposed in the boom cylinder circuit, and configured to control supply and discharge of hydraulic oil to and from the boom cylinder; an arm control valve (28, 29) disposed in the arm cylinder circuit, and configured to control supply and discharge of hydraulic oil to and from the arm cylinder; a boom operation means for operating the boom control valve; an arm operation means for operating the arm control valve (28, 29); a merging circuit connected to the boom cylinder circuit at a branch connection point upstream of the boom control valve in a state that the merging circuit is branched from the boom cylinder circuit, and configured to cause hydraulic oil discharged from the first hydraulic pump to merge with the arm cylinder; a boom operation detector for detecting a presence or absence of a boom lowering operation by the boom operation means; an arm operation detector for detecting a presence or absence of an arm pushing operation by the arm operation means; a merge switching valve disposed between the branch connection point of the merging circuit and the boom control valve in the boom cylinder circuit, and configured to be switchable between a supply position at which hydraulic oil is suppliable from the first hydraulic pump to the boom control valve, and a blocking position at which supply of hydraulic oil is blocked; a replenishing circuit including a replenishing valve for replenishing hydraulic oil in a tank to a rod side chamber of the boom cylinder; and a controller, characterized in that the controller is configured to switch the merge switching valve to the blocking position when a combined operation of a boom lowering operation and an arm pushing operation is detected by the boom operation detector and the arm operation detector. a boom attached to a base machine to be operable to be raised and lowered by pivotal movement around a boom foot pin; an arm attached to a distal end of the boom to be operable to be pushed and pulled; a boom cylinder for raising and lowering the boom; an arm cylinder for pushing and pulling the arm; a first hydraulic pump and a second hydraulic pump as a hydraulic source of the boom cylinder and of the arm cylinder; a boom cylinder circuit for connecting the first hydraulic pump and the boom cylinder; an arm cylinder circuit for connecting the second hydraulic pump and the arm cylinder; a boom control valve disposed in the boom cylinder circuit, and configured to control supply and discharge of hydraulic oil to and from the boom cylinder; an arm control valve (28, 29) disposed in the arm cylinder circuit, and configured to control supply and discharge of hydraulic oil to and from the arm cylinder; a boom operation means for operating the boom control valve; an arm operation means for operating the arm control valve (28, 29); a merging circuit connected to the boom cylinder circuit at a branch connection point upstream of the boom control valve in a state that the merging circuit is branched from the boom cylinder circuit, and configured to cause hydraulic oil discharged from the first hydraulic pump to merge with the arm cylinder; a boom operation detector for detecting a presence or absence of a boom lowering operation by the boom operation means; an arm operation detector for detecting a presence or absence of an arm pushing operation by the arm operation means; a merge switching valve disposed between the branch connection point of the merging circuit and the boom control valve in the boom cylinder circuit, and configured to be switchable between a supply position at which hydraulic oil is suppliable from the first hydraulic pump to the boom control valve, and a blocking position at which supply of hydraulic oil is blocked; a replenishing circuit including a replenishing valve for replenishing hydraulic oil in a tank to a rod side chamber of the boom cylinder; and a controller, characterized in that the controller is configured to switch the merge switching valve to the blocking position when a combined operation of a boom lowering operation and an arm pushing operation is detected by the boom operation detector and the arm operation detector.