In the elastic optical network, there has been the problem that processing steps increase that are required to re-optimize client signals to be concentrated; therefore, an optical network controller according to an exemplary aspect of the present invention includes reallocation detection means for monitoring an operation status of at least one of an optical communication channel and an optical node device that constitute an optical network, and determining, based on the operation status, whether or not to reallocate a client signal accommodated in an optical path set in the optical network; design-candidate exclusion means for designating, as a design exclusion object, at least one of the optical communication channel and the optical node device that are associated with an optical path targeted for reallocation that accommodates the client signal that the reallocation detection means has determined to reallocate; optical path design means for determining an alternative route for the optical path targeted for reallocation from among routes with the exception of the design exclusion object; traffic reference means for determining the client signal to be reaccommodated in an optical path on the alternative route, referring to demand traffic accommodated in the optical path targeted for reallocation; and line concentration design means for constituting line-concentration traffic in which traffic having been allocated to the alternative route and the demand traffic are concentrated, wherein the traffic reference means determines a reallocation optical path in which an optical path candidate with number of occupied wavelength slots increasing is excluded from optical path candidates on the alternative route, and the optical path design means determines wavelength allocation of the reallocation optical path so as to accommodate the line-concentration traffic.