A network camera system is configured such that an adapter device is connected with a digital camera, and the adapter device is connected with a network to which a client is also connected. A video signal representing a real-time image and a digital image signal representing a high-resolution still image are transmitted from the camera to the adapter. The adapter has a function of a file server and allows the client to download image data corresponding to the high-resolution still image. The adapter device further has a function of a streaming server and transmits streaming data representing the real-time image. The client can transmits an operation command to the adapter through the network, and the adapter transfer the command to the camera to perform the operation required by the client.