A radio device including a plurality of antennas transmitting and receiving a signal a reception band filter which controls a pass frequency band a measuring circuit which measures a reception level of the signal received by each of the plurality of antennas in a preamble in the signal received through the reception band filter an antenna switch which switches the plurality of antennas based on a measurement result from the measuring circuit and a processor which controls transmission and reception of the signal of the radio device and a pass frequency band of the reception band filter, and which transmits, based on a packet density, an instruction for changing the preamble from a first data length to a second data length to the other radio device and for changing the pass frequency band of the reception band filter from a first band to a second band.