An apparatus for designing an optical network having nodes, includes: a parameter holding unit which holds values of one or more optical-transmission parameters corresponding to one or more components constituting the optical network; a part generation unit which generates design candidates for a part to be arranged in each of one or more spans between the nodes so that each of the design candidates contains at least one of the one or more components; a part selection unit which makes a selection, for each of the one or more spans, of one of the design candidates which has at least one value of at least one of the one or more optical-transmission parameters satisfying a design condition; and a construction control unit which constructs the optical network by combining one or more parts each of which is selected by the part selection unit.