A unit connectable to a PLC, Programmable Logic Controller,, the unit comprising: a communication unit for relaying communication between an external device connected to a first network and a function unit connected to a second network; a setting unit for acquiring address information of the function unit in the second network from the function unit, and generating setting information in which the address information is associated with an identifier of the function unit that substitutes for the address information; and a link information generation unit generating link information used for accessing information in the function unit from the external device based on an address information of the unit and the identifier of the function unit in response to receiving an acquisition request for a portal site from the external device, wherein the link information comprises an URL in the first network and a hyperlink of each of one or more applications provided by the function unit, and the unit is configured to acquire application-specific access right information from the function unit and acquire user-specific access right information comprising a type of access right given to a user who has logged in to the external device with login information from the external device; in response to receiving the acquisition request from the external device, acquire login information of a user and a first identifier included in the acquisition request; acquire the address information corresponding to the first identifier with reference to the setting information; specify a type of access right given to the user with the acquired login information based on the user-specific access right information, and specify each of the one or more applications that can be accessed with the type of access right of the user based on the application-specific access right information; transmit the link information including the hyperlinks of the one or more applications to which the user has the access right to the external device; and in response to receiving a first access request including the URL associated with the hyperlink of the application to which the user has access right and selected from the portal site by the user from the external device, acquire a second identifier included in the first access request and the address information corresponding to the second identifier, generate a second access request by replacing the second identifier included in the first access request with the address information, access the application in the function unit to acquire target information as an HTML document based on the second access request, and transmit the HTML document to the external device. a communication unit for relaying communication between an external device connected to a first network and a function unit connected to a second network; a setting unit for acquiring address information of the function unit in the second network from the function unit, and generating setting information in which the address information is associated with an identifier of the function unit that substitutes for the address information; and a link information generation unit generating link information used for accessing information in the function unit from the external device based on an address information of the unit and the identifier of the function unit in response to receiving an acquisition request for a portal site from the external device, wherein the link information comprises an URL in the first network and a hyperlink of each of one or more applications provided by the function unit, and the unit is configured to acquire application-specific access right information from the function unit and acquire user-specific access right information comprising a type of access right given to a user who has logged in to the external device with login information from the external device; in response to receiving the acquisition request from the external device, acquire login information of a user and a first identifier included in the acquisition request; acquire the address information corresponding to the first identifier with reference to the setting information; specify a type of access right given to the user with the acquired login information based on the user-specific access right information, and specify each of the one or more applications that can be accessed with the type of access right of the user based on the application-specific access right information; transmit the link information including the hyperlinks of the one or more applications to which the user has the access right to the external device; and in response to receiving a first access request including the URL associated with the hyperlink of the application to which the user has access right and selected from the portal site by the user from the external device, acquire a second identifier included in the first access request and the address information corresponding to the second identifier, generate a second access request by replacing the second identifier included in the first access request with the address information, access the application in the function unit to acquire target information as an HTML document based on the second access request, and transmit the HTML document to the external device.