To charge surely depending on data transmitted through a TCP/IP communication network or the like with a simple configuration. In charging method for data transmission in a communication network in which a plurality of positions are connected to each other through a wide area network, sub-networks being connected to the respective positions through LANs, and sending of data from terminal stations in the sub-networks or receiving of data in the terminal stations being performed, sampling measurements of transmission states of originated data in the LANs and transmission states of incoming data in the LANs are performed in the LANS connected to respective positions, the data of the transmission states subjected to the sampling measurement being periodically transmitted to a predetermined center connected to the communication network, and an amount of charging to each sub-network being decided on the basis of the data of the transmission states transmitted to the center.