A communication band calculation device includes a memory; and a processor configured to execute acquiring user-based traffic information; defining non-overlapping separate section columns having any section width as a state space and sets a user distribution of a traffic amount according to the state space based on the traffic information; generating a transition probability matrix in which a transition probability that a transition from a separate section to another in the state space occurs is set as an element based on the traffic information; obtaining prediction of the user distribution at a desired future time using a product of the user distribution which is a starting point of prediction and the transition probability matrix; and calculating an amount of band facilities required to achieve quality of a communication service at a future point in time based on the user distribution in future.