This invention provides a simultaneous packet transmission system and a simultaneous packet reception system which enable a reception side to receive simultaneous packets without transmitting a retransmission request to retransmit discarded simultaneous packets even if part of simultaneous packets are discarded. A wireless LAN base station multicasts a simultaneous packet which is obtained by allocating a sequence number to a LAN packet a plurality of times. If a wireless LAN terminal receives the same simultaneous packets a plurality of times, the wireless LAN terminal discards duplicated simultaneous packets and leaves only one simultaneous packet. Since the simultaneous packet is multicast a plurality of times, the wireless LAN terminal can receive the simultaneous packet as long as all the same simultaneous packets are not lost.