When an optical path arrangement is re-arranged, the packet loss amount is reduced by judging whether to perform the shift in one stage or whether to perform the shift in two stages in accordance with the state of the network. This is implemented by an optical communication network comprising a plurality of routers, a plurality of optical switches, optical fiber connecting the routers and optical switches or connecting the optical switches, and a management device. First, the first evaluation value is determined by evaluating the packet loss amount resulting from a one-stage shift. Thereafter, when the optical path arrangement is changed by means of a two-stage shift, the optical path group to be changed is divided into two, one optical path group is selected as the first-order shift optical path, and the other optical path group is made the second shift optical path. Thereafter, a second evaluation value is established by evaluating the packet loss amount when shifting the optical path arrangement by means of a two-stage shift. When the second evaluation value is smaller than the first evaluation value, the first evaluation value is substituted by the second evaluation value. The above steps are repeated until the processing termination condition is satisfied.