In this paper, to improve the efficiency of state exploration and to relieve the problem of state explosion, we propose another method of state exploration called the extended circular exploration (ECE), which does not need to explore all the reachable global states and can be applied to N(N greater-than-or-equal-to 2)-party protocol with alternative routes, i.e. it is applicable to the protocol in which adaptive routing mechanism can be performed. Using this ECE, we can eliminate the topology restriction of the circular exploration (CE) through extending the notion of circular exploration. We explore only those global states which are reachable, provided that the participant processes of any group of transitions proceed at the same speed, and that they can be formed as a cycle. The state space thus explored is not exhaustive. The algorithm presented can detect deadlock error and unspecified reception error. It requires storage space and/or execution time much less than those of the conventional perturbation method. It can be viewed as a solution of the N-process collision and the interference mechanism.