Disclosed is a method of recognizing an available channel in order to prevent channel occupation requirements from colliding with each other when one wireless channel is shared by plural terminals in a CSMA/CA mechanism using an IEEE 802.15.4 protocol slot, the method including: a first step of initializing a counter, CW, as 2, the CW being used for CCA which an attempt to perform is made before frame transmission; a second step of determining if a required channel is occupied; a third step of decreasing the CW by 1 when the channel is idle in the second step; a fourth step of re-determining if the channel is occupied; and a fifth step of, based on a determination result in the fourth step, determining if the CW is 1 when the channel is occupied.