A method of opening a network in a manufacturing system, the system including a plurality of robots, a plurality of robot controllers individually controlling the robots and a plurality of networks connecting the robot controllers with each other. The method includes the steps of opening a first network to the plurality of robot controllers, by setting, in each of the plurality of robot controllers, conditions, including addresses, required for opening the first network; designating an address range prepared in the first network for robot controllers to which a second network is opened and which is selected from among the plurality of robot controllers; and opening the second network to the robot controllers addressed within the address range designated in the first network, by setting, through the first network, conditions required for opening the second network.