Provided is a request processing method of processing a request requesting task processing in a computer system including the steps of: transmitting, by a proxy server, a first requests which is one of duplicate and original requests to application servers; transmitting, by the application servers, a result of processing of the first requests to the proxy server; notifying, by the application servers, a session management server of session information including identifiers of the application servers and identifiers of the first requests; determining, by the proxy server, a result of the processing used for responding to a client computer upon receiving the result of the processing of the first requests; and notifying, by the proxy server, the session management server of the identifiers of the application servers which have transmitted the determined processing result and an identifier of the request transmitted from the client computer.