A transaction processing apparatus includes a display unit, a base unit, and an attaching and detaching unit that connects circuits of the display unit and the base unit. The display unit includes an authentication-information acquiring unit that acquires, in a state in which the display unit is detached from the base unit, identity authentication information of a customer and an authentication-information storing unit that stores the acquired identity authentication information. The base unit includes a registered-information acquiring unit that acquires registered authentication information that should be compared with the identity authentication information, an identity authentication unit that performs identity authentication on the basis of the identity authentication information stored by the authentication-information storing unit and the registered authentication information acquired by the registered-information acquiring unit, and a card-settlement permitting unit that permits card settlement when a result of the identity authentication is affirmative.