A control method performed in an electric power transaction system including: first electric power equipment, comprising solar photovoltaic power generation equipment or gas electric power generation apparatus or wind electric power generation apparatus, which is used by a first user; second electric power equipment, also comprising solar photovoltaic power generation equipment or gas electric power generation apparatus or wind electric power generation apparatus, which is used by a second user; and a plurality of servers (200a 200b 200c) which are connected to the first electric power equipment and the second electric power equipment via a network so as to enable communication with each other, the control method being executed by a first server included in the plurality of servers and comprising: receiving first transaction data from the first electric power equipment via the network, the first transaction data including: a first blockchain address which is an identifier for identifying at least one of the first user and the first electric power equipment; electric power selling amount information indicating an amount of electric power which can be sold by the first electric power equipment; and a first electronic signature associated with the first user; verifying whether the first electronic signature included in the first transaction data received is valid; verifying validity of the first transaction data received; when the first electronic signature and the validity of the first transaction data are verified successfully, executing a first consensus algorithm for reaching a consensus that validity of the first transaction data is verified, together with a plurality of second servers different from the first server among the plurality of servers; and when the consensus that the validity of the first transaction data is verified was reached according to the first consensus algorithm, recording a block including the first transaction data in a distributed ledger of the first server, characterized in that the first electronic signature is a first group signature assigned to a first group of users including the first user, such that the first group signature is configured to enable verification that the group signature was provided by a group member including the first user while disabling identification of the group member and, the first transaction data further includes a first time stamp indicating a date and time period during which the electric power can be sold, and said first group signature is generated by the first electric power equipment by means of a signature generator, based on the electric power selling amount information, using a signature generating key for the first user, the signature generating key being obtained from a service server by the first electric power equipment and being a secret key for providing a group signature, the service server being different from the first server and being connected via the network. receiving first transaction data from the first electric power equipment via the network, the first transaction data including: a first blockchain address which is an identifier for identifying at least one of the first user and the first electric power equipment; electric power selling amount information indicating an amount of electric power which can be sold by the first electric power equipment; and a first electronic signature associated with the first user; verifying whether the first electronic signature included in the first transaction data received is valid; verifying validity of the first transaction data received; when the first electronic signature and the validity of the first transaction data are verified successfully, executing a first consensus algorithm for reaching a consensus that validity of the first transaction data is verified, together with a plurality of second servers different from the first server among the plurality of servers; and when the consensus that the validity of the first transaction data is verified was reached according to the first consensus algorithm, recording a block including the first transaction data in a distributed ledger of the first server, characterized in that the first electronic signature is a first group signature assigned to a first group of users including the first user, such that the first group signature is configured to enable verification that the group signature was provided by a group member including the first user while disabling identification of the group member and, the first transaction data further includes a first time stamp indicating a date and time period during which the electric power can be sold, and said first group signature is generated by the first electric power equipment by means of a signature generator, based on the electric power selling amount information, using a signature generating key for the first user, the signature generating key being obtained from a service server by the first electric power equipment and being a secret key for providing a group signature, the service server being different from the first server and being connected via the network.