An information-processing device, comprising: a mobile terminal having a first terminal; at least one mobile reading unit (5, 73) having a second terminal (47, 77), the reading unit (5, 73) being configured to read data from an information medium (71, 88); and a mobile connection unit configured to connect the mobile terminal and the reading unit (5, 73), wherein the mobile terminal is a smartphone or a tablet PC, the connection unit including a first terminal portion configured to contact the first terminal of the mobile terminal for electrical connection with the mobile terminal, a second terminal portion configured to contact the second terminal (47, 77) of the reading unit (5, 73) for electrical connection with the reading unit (5, 73), an electrical pathway (25, 27) disposed between the first terminal and the second terminal (47, 77) to connect the mobile terminal and the reading unit (5, 73), and a main body having a rectangular plate part to be disposed along a rear face side of the mobile terminal, the reading unit (5, 73) being attached to and detached from the main body in a state in which the rectangular plate part of the main body is disposed along the rear face side of the mobile terminal, the main body including a first body portion where the first terminal portion is disposed and a second body portion, other than the first body portion, where the second terminal portion is disposed, and the main body being disposed between the mobile terminal and the reading unit (5, 73) with being sandwiched therebetween when the reading unit (5, 73) is attached to the main body in a state in which the rectangular plate part of the main body is disposed along the rear face side of the mobile terminal, characterized in that the plate-shaped surface of the connection unit is smaller in size than the rear face side of the mobile terminal. a mobile terminal having a first terminal; at least one mobile reading unit (5, 73) having a second terminal (47, 77), the reading unit (5, 73) being configured to read data from an information medium (71, 88); and a mobile connection unit configured to connect the mobile terminal and the reading unit (5, 73), wherein the mobile terminal is a smartphone or a tablet PC, the connection unit including a first terminal portion configured to contact the first terminal of the mobile terminal for electrical connection with the mobile terminal, a second terminal portion configured to contact the second terminal (47, 77) of the reading unit (5, 73) for electrical connection with the reading unit (5, 73), an electrical pathway (25, 27) disposed between the first terminal and the second terminal (47, 77) to connect the mobile terminal and the reading unit (5, 73), and a main body having a rectangular plate part to be disposed along a rear face side of the mobile terminal, the reading unit (5, 73) being attached to and detached from the main body in a state in which the rectangular plate part of the main body is disposed along the rear face side of the mobile terminal, the main body including a first body portion where the first terminal portion is disposed and a second body portion, other than the first body portion, where the second terminal portion is disposed, and the main body being disposed between the mobile terminal and the reading unit (5, 73) with being sandwiched therebetween when the reading unit (5, 73) is attached to the main body in a state in which the rectangular plate part of the main body is disposed along the rear face side of the mobile terminal, characterized in that the plate-shaped surface of the connection unit is smaller in size than the rear face side of the mobile terminal.