To enable different platform terminal devices to stably continue a service when providing a service to a plurality of platforms.

A platform service system is provided with platform service systems(100a, 100b) for providing a service through a network in accordance with access from terminal devices (110a, 110b) of customers and a service device (150) installed in the platform service systems (100a, 100b) for providing the service to the terminal devices of the customers. Access from the terminal device is transmitted through the platform service systems to which the terminal device is belonging at least one time, and to information data to be transmitted from the platform service systems to the service device, an identifier is attached to recognize that the information data have been transmitted from the terminal device, and the service device identifies the plurality of platform service systems, plurality of networks, and a plurality of terminal devices.