A base station calculates the number of terminals which have transmitted messages at ith frame, and calculates the number of messages to be transmitted at (i+1)th frame by using the number of terminals which have transmitted the messages in the ith frame. The base station calculates a transmission probability by using the number of messages to be transmitted in the (i+1)th frame and the number of random access slots, and transmits the number of messages to be transmitted in the (i+1)th frame and the transmission probability to the plurality of terminals. The base station receives a message transmitted by a pertinent terminal, whose number of messages to be transmitted in the (i+1)th frame is greater than the number of random access slots, among the plurality of terminals, according to the result obtained by comparing the transmission probability and a random number.