A wireless communication system, comprising: a first device configured to repeatedly transmit data within a specific transmission time; and a second device configured to perform intermittent reception by repeating a specific reception duration at a constant period in order to receive the data from the first device, wherein the second device has: a transceiver configured to transmit and receive the data to and from the first device; a packet data number confirmation component configured to confirm the number of a plurality of packet data included in the data received by the transceiver; a packet data number comparator configured to compare the number of a plurality of packet data included in the data received by the transceiver with a total number of packet data to be sent out from the first device in a single transmission; and is characterized by an extension time calculator configured to calculate an extension time of the reception duration of the transceiver from the difference between the total number of packet data to be sent out from the first device and the number of a plurality of packet data included in the data received by the transceiver on the basis of the comparison result of the packet data number comparator, and from a transfer rate between the first device and the second device; and a reception duration controller configured to extend the specific reception duration according to the extension time. a first device configured to repeatedly transmit data within a specific transmission time; and a second device configured to perform intermittent reception by repeating a specific reception duration at a constant period in order to receive the data from the first device, wherein the second device has: a transceiver configured to transmit and receive the data to and from the first device; a packet data number confirmation component configured to confirm the number of a plurality of packet data included in the data received by the transceiver; a packet data number comparator configured to compare the number of a plurality of packet data included in the data received by the transceiver with a total number of packet data to be sent out from the first device in a single transmission; and is characterized by an extension time calculator configured to calculate an extension time of the reception duration of the transceiver from the difference between the total number of packet data to be sent out from the first device and the number of a plurality of packet data included in the data received by the transceiver on the basis of the comparison result of the packet data number comparator, and from a transfer rate between the first device and the second device; and a reception duration controller configured to extend the specific reception duration according to the extension time. a transceiver configured to transmit and receive the data to and from the first device; a packet data number confirmation component configured to confirm the number of a plurality of packet data included in the data received by the transceiver; a packet data number comparator configured to compare the number of a plurality of packet data included in the data received by the transceiver with a total number of packet data to be sent out from the first device in a single transmission; and is characterized by an extension time calculator configured to calculate an extension time of the reception duration of the transceiver from the difference between the total number of packet data to be sent out from the first device and the number of a plurality of packet data included in the data received by the transceiver on the basis of the comparison result of the packet data number comparator, and from a transfer rate between the first device and the second device; and a reception duration controller configured to extend the specific reception duration according to the extension time.