Abstract: A dynamic maintenance planning apparatus including a maintenance planning device and a priority calculating device is provided. The maintenance planning device determines a maintenance date and time on and at which the throughput of a manufacturing system is maximum from among possible maintenance dates and times based on a simulation result in which a specific manufacturing apparatus on a manufacturing system is stopped at a specified maintenance date and time, and, for the maintenance at the determined maintenance date and time, specifies a lot whose completion is predicted to be delayed. The priority calculating device calculates a priority of the lot whose completion is predicted to be delayed so as to prevent waiting time of the lot during the maintenance.