To improve communication throughput by enabling fist response.

In a lower layer, a step A1 detects the occurrence of an event that externally comes, a step A3 notifies an upper layer of the occurrence of the event and also, a step A4 responds according to a correspondence method that is stored in an event table and sends a response message. In the upper layer, a step B1 receives an event occurrence notification that is sent from the lower layer, a step B3 creates a response message and sends it to the lower layer to instruct it and a step B4 processes each notification and also updates the event table.