A hydraulic control device of construction machinery is disclosed. The device includes a main merging/diverging valve, operating levers operated to actuate plural actuators, an operating condition judging section, and a pattern collating section. When a load pressure of each actuator is high, a discharge pressure of each discharge oil path is also high, and when a total of the discharge pressures exceeds a predetermined set pressure, the main merging/diverging valve is switched to a diverging position, and when the total of the discharge pressures drops to below the set pressure, the main merging/diverging valve is switched to the merging position.