A path selection method, an information processor, a network system, and a path selection program are provided which rapidly determine a path that has no loop when determining the path by using a control server to probabilistically select a pass node. A network having a plurality of paths from a source to a destination is controlled. A node forming the path is selected on the basis of a node-to-node transfer probability, and in the case where the selected node is a node that has already been passed through on the path, the transfer probability is reset such that the selection of the node is suppressed.