An initiator device is provided with a generation circuit for supporting Single User (SU)-Multiple Input Multiple Output (MIMO) operation and generating a first signal including a value that indicates which of a reciprocal MIMO phase and a non-reciprocal MIMO phase is to be applied to SU-MIMO BF training, and a transmission circuit for transmitting the first signal to a responder device. The responder device is provided with a reception circuit for receiving the first signal from the initiator device, and a processing circuit for determining on the basis of the value which of the reciprocal MIMO phase and the non-reciprocal MIMO phase is to be applied to SU-MIMO BF training.