Abstract: For managing a production line which includes a plurality of facilities for carrying out a production process to produce products of a target quantity, use is made of a production simulator (22). In managing the production line, the production simulator makes the production process have a virtual stop period for a selected one of the facilities. The production simulator executes a simulation of the production process excepting the virtual stop period to produce a simulated quantity. With the simulated quantity being compared with the target quantity, the production simulator produces an allowed stop period of the production process so that the allowed stop period uninfluences on the target quantity. Therefore, it is possible to stop the selected facility during the allowed stop period.