Provided are a reciprocal distribution calculating method and a reciprocal distribution calculating system for cost accounting, in which, when performing cost accounting using a computer, a reciprocal distribution method is used to effectively perform cost accounting of each department. In the reciprocal distribution calculating method and the reciprocal distribution calculating system for cost accounting, reciprocal distribution costs are calculated using the limit and convergence of a transition probability matrix. And, a reciprocal distribution calculation is performed in a completely different way from the method of calculating reciprocal distribution known for the last several tens of years and in an effective manner, thereby calculation of reciprocal distribution costs at a high speed.