A communication apparatus includes receiving means for receiving image data and accompanying communication information, primary storage means for temporarily storing them, secondary storage means having a greater storage capacity than the primary storage means, forwarding means for converting the image data to a standard format and forwarding it with the communication information, network communication means for transmitting the standard format image data with the communication information to the server apparatus. The communication apparatus further includes retransmitting means operable in case of a failure of transmission. The retransmission means saves the image data and communication information stored in the primary storage means in the secondary storage means, deletes the image data from the primary storage means, converts the saved image data into a standard format, retransmits the standard format image data to the server apparatus with the communication information and repeats retransmission in case of a failure of the preceding retransmission.