A transmission device can be carried by the subject. A biological signal recording device can perform wireless communication with the transmission device. A transmitter transmits biological signal data corresponding to a biological signal of a subject. A storage stores the biological signal data. A receiver receives the biological signal data. A recorder records the biological signal data received by the receiver. A detector detects a missing portion in the biological signal data recorded by the recorder or a receipt of the biological signal data by the receiver. A notifier notifies the missing portion or transmits an acknowledgment of the receipt to the transmission device. A complementary transmitter retrieves biological signal data corresponding to the notified missing portion from the storage or identifies unreceived biological signal data and retrieves the identified biological signal data, and transmits the retrieved biological signal data. A complementary recorder records the biological signal data transmitted by the complementary transmitter.