An importance level determination unit receives: input from a camera of frames of moving images taken; input from a switch connected to a server which is operated manually by hand; and voice input from a microphone. Based on these it determines the importance level of each image frame. An encoder compresses and encodes the image frames obtained by the camera and generates moving picture streams. A packetizer packetizes the moving picture streams and gives them to a tag attachment unit. The tag attachment unit attaches the importance level set for the respective image frames to packet headers of the moving picture streams as a priority tag. A transmission unit transmits packets with a priority tag to a network which includes a router with a packet priority control function.