A management system, a management method, an information processing device, and an information processing method, which apply a communication technology that uses the human body as a communication medium to a vehicle or a building that allows multiple people to sit on designated seats, and can support passengers and people entering the venue management. The passenger management system (1000) is composed of a train management device (1004), a guidance device (1006), and a seat device (1008) provided on each seat. The guidance device reads ticket information (information such as a bus ticket, a reserved seat ticket, etc.) from a user device worn by a passenger, and provides guidance on seats and the like. After confirming whether there is a seater, the seat device reads the ticket information from the user equipment worn by the seater, judges the legitimacy of the ticket, and notifies the management device of the seat information indicating that the seat is empty, has been retrieved, or does not carry a ticket. In addition, we sell ticket to seated person. The present invention can be applied to trains, airplanes, stadiums, theaters and the like.