A chat system comprises editor 1 which includes an input area for chatting and an output area where chat conversation is written; information converter 2 which is capable of reading an inputted character string written into the editor 1 and detecting a specific input, and outputting an input to an input area in the editor 1, and reads a character string existing in the editor 1, converts the character string to a code and add to control information for a chat; transmitter 3 which transmits information outputted from the information converter 2 to a chat communication partner; receiver 4 which receives information sent from the chat partner; and information analyzer/converter 5 which analyzes and converts a code to a character string, outputs the character string onto the output area in the editor 1, and performs an operation in accordance with the control information.