A group determination method includes a step of calculating an external set-up work time for an external set-up work by which a component supplier used in a group that is a next production target of a group under production in a component mounting line, including a plurality of the component mounters capable of attaching and detaching a component supply carriage which can arrange a plurality of the component suppliers (tape feeders), is removed from the component mounting line and arranged in the component supply carriage; and a step of calculating a production completion time at which the production of all the mounting boards that are the production targets is completed in consideration of the external set-up work time. A plurality of groups which are common in an arrangement of component suppliers for the mounting boards that are the production targets are determined so that production completion time is shortened.