The safety is improved when executing a transaction instructed after the login from a user having carried out the login operation to the server. A transaction system (101) includes a server (121), a first terminal (141), and a second terminal (161). A user logs-in the server (121) through the first terminal (141). The server (121) generates a notice to be transmitted to the second terminal (161) when receiving an instruction of a transaction through the first terminal (141) from a user. The first terminal (141) or the second terminal (161) prompts the user to input a confirmation of details of the transaction when the notice is transmitted to the second terminal (161) from the server (121). The server (121) regards the confirmation of the transaction made by the user as having been made when the input of the user matches with the details of the transaction.