A water-soluble and biodegradable antimicrobial agent is provided, comprising a polymer composed of a segment A and a segment B, in which, the segment A has the following formula I:the segment B has the following formula II:wherein the segment A and the segment B in the polymer have a molar ratio of 1:0. One end of said capacitor element is connected by way of said nonvolatile memory element to a potential supply line. Owing to this, by just mounting the keyboard unit in the PC body, the connector is connected to the connector in the PC body side, and hence connection becomes simple. If the message has not previously been sent, the messaging server corrects the message and sends the corrected message and the message ID to the recipient client system.