1. A non-transitory computer readable medium containing instructions of a common parameter interface generation program, which generates a common parameter interface in a line design tool which generates line design information of a control system having models of control devices arranged therein, a mechanical design tool which selects a control device on the basis of the line design information and generates mechanical design information, and a control design tool which generates control design information of a mechanical operation on the basis of the mechanical design information, that, when executed by a computer, cause the computer to perform: assigning identification information for identifying the control device in the line design information; acquiring a list of parameters of the selected control device, which are used in the mechanical design information and the control design information, from a design information storage unit; associating the acquired list of the parameters with the identification information and names of the selected control device in each of the line design information, the mechanical design information, and the control design information to generate a common parameter and registering the common parameter in a common parameter storage unit that stores a parameter used in common by the line design tool, the mechanical design tool and the control design tool, the names of the selected control device being different from each other in the line design information, the mechanical design information, and the control design information; and generating, in each of the line design tool, the mechanical design tool, and the control design tool, a common parameter interface that acquires a value of one of the parameters of the selected control device from the common parameter storage unit when one of the line design information, the mechanical design information, and the control design information is read and reads out the value of the parameter to the one of the line design information, the mechanical design information, and the control design information in a data format in data format definition information which defines the data format required when the parameter is treated in the line design tool, the mechanical design tool, and the control design tool, wherein the line design tool, the mechanical design tool, and the control design tool use different data formats from each other to treat the parameter, and the generating further comprises converting the data format to one of the different data formats based on the data format definition information.