Abstract: In a data communication system for carrying out data communication and a radio communication apparatus, especially in a structure including a data transmitting part for transmitting data through a radio link, and a data receiving part for sending back a receipt acknowledgment signal to notify reception, this invention is characterized in that a control is carried out so that in a case where the receipt acknowledgment signal can not be obtained because of quality degradation of the radio link, or in a case where the receipt acknowledgement signal can not be obtained because of handover in a data communication using a mobile, a pseudo receipt acknowledgment signal is used to avoid a reduction of throughput from the data transmitting part, which occurs in the case where the receipt acknowledgment signal can not be obtained.