PURPOSE: To automatically switch modes without performing complicated operations by discriminating whether or not the transmission of light is interrupted by an original covering sheet and switching to the circuit of a CCD sensor for either transmission or reflection.

CONSTITUTION: A reflection unit 1 incorporates the reading means of a reflective original. Then, a scanner 100 is provided with the CCD sensor 8 for the reflection for reading the reflective original on a light source side and the CCD sensor 9 for the transmission for reading a transmissible original on the opposite side with an original platen 5 there between. When the power source of a scanner light source 7 is turned ON, the light source 7 is lighted and since the original covering sheet 6 is opaque when the sheet 6 is mounted on the side of an unit 2 for the transmissible original, the light of the light source 7 is interrupted and does not reach the sensor 9. Then, whether or not the transmission of the light is interrupted is discriminated by a transmission connection means 13, a circuit changeover switch 10 is automatically switched correspondingly and the light reaches the sensor 8 or 9. Thus, the mode can be automatically switched without the complicated attaching and detaching operation of the units 1 and 2.