A component mounting line design device, comprising: a storage section which stores component mounting line information for identifying, for each board type, an order of arranging a component mounting device (130: 130A, 130B) in producing a relevant type of board, a position where a mounting head (145A, 145B) is attached to the component mounting device (130: 130A, 130B), a type of the mounting head (145A, 145B) mounted at the position, and a type of a component feeder device (140, 151, 153) of the component mounting device (130: 130A, 130B); and a control section, wherein the control section is configured to prepare board groups of board types, and calculate, for each pair of the board groups of the board types, an amount of work in changing a component mounting line identified by component mounting line information corresponding to one board type contained in one board group contained in the pair to a component mounting line identified by component mounting line information corresponding to other board type contained in other board group contained in the pair, the amount of work is a work time required to change a component mounting line configuration, the change work time is calculated according to at least one of, or an arbitrary combination of the number of the component mounting devices contained in a component mounting line, the type of a mounting head attached to the component mounting device and the number thereof, and the type of a component feeder device used in the component mounting device and the number thereof as well as the mounting / demounting times of the component mounting devices, the mounting heads and the feeder types, the control section is further configured to initialize a set of board groups with all the board groups, select a board group including boards produced in a current line configuration, as a board group to produce first, repeat while the set of board groups is not empty deleting the lastly selected board group (g) from the set of board groups, selecting, among the set of board groups, a board group which the amount of change work from the lastly selected board group (g) is the minimum, as a board group to produce next, and thereby identify an order of putting into the component mounting line of the board type so that a total value of the amount of work becomes minimum. a storage section which stores component mounting line information for identifying, for each board type, an order of arranging a component mounting device (130: 130A, 130B) in producing a relevant type of board, a position where a mounting head (145A, 145B) is attached to the component mounting device (130: 130A, 130B), a type of the mounting head (145A, 145B) mounted at the position, and a type of a component feeder device (140, 151, 153) of the component mounting device (130: 130A, 130B); and a control section, wherein the control section is configured to prepare board groups of board types, and calculate, for each pair of the board groups of the board types, an amount of work in changing a component mounting line identified by component mounting line information corresponding to one board type contained in one board group contained in the pair to a component mounting line identified by component mounting line information corresponding to other board type contained in other board group contained in the pair, the amount of work is a work time required to change a component mounting line configuration, the change work time is calculated according to at least one of, or an arbitrary combination of the number of the component mounting devices contained in a component mounting line, the type of a mounting head attached to the component mounting device and the number thereof, and the type of a component feeder device used in the component mounting device and the number thereof as well as the mounting / demounting times of the component mounting devices, the mounting heads and the feeder types, the control section is further configured to initialize a set of board groups with all the board groups, select a board group including boards produced in a current line configuration, as a board group to produce first, repeat while the set of board groups is not empty deleting the lastly selected board group (g) from the set of board groups, selecting, among the set of board groups, a board group which the amount of change work from the lastly selected board group (g) is the minimum, as a board group to produce next, and deleting the lastly selected board group (g) from the set of board groups, selecting, among the set of board groups, a board group which the amount of change work from the lastly selected board group (g) is the minimum, as a board group to produce next, and thereby identify an order of putting into the component mounting line of the board type so that a total value of the amount of work becomes minimum.