The present invention ensures safety and validity, during generation of encryption keys required for encrypted communication between an overall control unit for an automatic transaction device and an internal device. An automatic transaction device comprising a first device mounted internally and a control unit that controls devices sends and receives data between said first device and the control unit. The first device executes processing that generates a first code relating to the first device and sends same to the control unit and executes processing that verifies a second code received from the control unit and generates an encryption key in accordance with the verification results. The control unit executes: processing whereby, after the first code has been received, verification is made that the operation environment is within the automatic transaction device; and processing whereby, if a determination is made that the operation environment is within the automatic transaction device, a second code is generated and sent to the first device.