A channel scanning apparatus in a portable Internet system establishes a radio link with each of neighboring access points without disconnecting a wireless link with a serving access point and collects radio channel state information of each of the respective neighboring access points. That is, apart from a RF signal processing unit that processes a radio signal from the serving access point, the channel scanning apparatus includes a dedicated scanning processing unit for processing a radio signal of a neighboring access point and measuring radio channel state information of the neighboring access point from the radio signals received by the dedicated scanning processing unit, and collects radio channel state information of the respective neighboring access points. In such a way, communication with the serving access point is not disconnected, and therefore the access terminal and the serving access point do not need to buffer traffic data.