An operation instructing system includes an individual process information obtaining section obtaining, each time a production element is entered into the system, the process information about one of the production lines to produce the entered production element; a state information obtaining section obtaining, on the basis of the process information, state information about remaining production processes the production elements currently in the production system; a determining section determining, each time operation completion report is obtained, the next manual step by the operator completed a manual step as a next operation step on the basis of the state information; and a notifying section notifying the operator of the next operation step. Accordingly, even when preferential degrees of operations randomly vary, operation shares of respective operators are clearly determined and the next operation steps are accurately notified to respective operator, so that the production efficiency can be improved.