PURPOSE: To prevent an input operation error at the time of continuous scannint by executing information corresponding to the number of data in a memory so that quantity of a data stored in the memory or its residual quantity can be confirmed.

CONSTITUTION: Light emitting diodes LED1WLEDn are provided linearly on the outside surface of a hand scanner 1 containing a light emitting element and a photodetector, a reflected ray from a bar-code is read by the scanner 1, is digitized by an A/D converting circuit 2 and is inputted to a pulse detecting circuit 3. By this circuit 3, a pulse synchronizing with fall and rise of an input square wave is detected, and an interrupt signal is inputted to a CPU5. A buffer memory 6 for storing an address of a memory M, a time counter TC and FFs I , IIare connected to this CPU5. In this state, whenever a data is written and read out to and from the memory M, LED1WLEDn are turned on or turned off through a display buffer circuit 9 and a decoder 10, so that quantity of the data of the memory M can be confirmed, by which generation of an input operation error is prevented.