Abstract: To provide a material monitoring system for biomass plastic from its source, information, such as weight, mass, or volume, in each nth node is transmitted at prescribed in and out timings to a central management server. Based on the information, the management server carries out monitoring of the original material's mass or volume which is presently onsite at the nth node. While material distribution elements will in reality branch off and become complex, the total quantity of the original material which the management server manages does not change. Should an error arise in a change in the total quantity of the original material which the management server manages, it will be possible to suspect an illicit event and to investigate the cause thereof based on the management information.