A hydraulic system with an improved complex operation is provided, which can prevent the generation of shock in a boom by delaying pressure supply during start and end of pilot signal pressure supplied to a spool for controlling an option device when a boom ascending operation and an operation of an option device are simultaneously performed or when such a simultaneous operation of the boom and the option device switches over to an independent operation of the boom. The hydraulic system with an improved complex operation includes main hydraulic pumps and a pilot pump; a boom cylinder and an option device; a main control valve including a boom spool and an option device spool which are shifted by a pilot signal pressure from the pilot pump; an operation lever which controls the boom spool; an option operation pedal which controls the option device spool; a confluence spool for controlling the option device; and a controller which outputs an electric control signal to a proportional control valve for the option device so as to delay pilot signal pressure supplied to the confluence spool during start and end of the pilot signal pressure supply when a complex operation for simultaneously operating the boom cylinder and the option device is performed.