To prevent leakage of data and falsification of data in a communication unit at a data transmission side or a communication unit at a data receiver side.

The communication unit includes: an HD 170 for storing received encrypted data; an HD 160 for storing the transmitted encryption data; an information processing apparatus 110 for writing the received encrypted data in the HD 170 and for reading the encrypted data being a transmission object from the HD 160; an information processing apparatus 120 for reading the encrypted data stored in the HD 170 and decrypting the encrypted data by using a private key; an authentication means 130 for authenticating a password attached to the data decrypted by the information processing apparatus 120 and a password transmitted in advance; an information processing apparatus 130 for reading the encrypted data which are stored in the HD 170 and the password of which is confirmed for the coincidence with the password transmitted in advance by the authentication means 130, and writing the encrypted data being the transmission object to the HD 160; and a reset means 123 for resetting the encrypted data read by the information processing apparatus 120.