A device includes a definition unit which defines a directional graph having a grid point as a node and a line connecting adjacent grid points as a branch, a generation unit which sets a branch connecting a grid pointing a wiring prohibited area in the branches of the directional graph to the capacity of “0”, and which sets another branch to the capacity of “1”, and which connects the starting point or the end point to each grid point of the wiring terminal indicated by wiring information, thereby generating a flow network, a search unit which searches the flow network for a path of a flow having the maximum amount of flow from the starting point to the end point, and a determination unit which determines a wiring path connecting the grid point indicated by the wiring information according to the search result of the path.