Optical coordinate input apparatus

In an optical coordinate input apparatus, an insect or mud may disturb optical coordinate input operation for a main computer. To avoid such a problem, light emitting element arrays and light receiving element arrays are arranged opposite to each other, a pair of these light emitting element and light receiving element are sequentially driven by a multiplexer, and a coordinate signal is output by a signal detecting device when an optical signal derived from the driven light emitting element cannot be received by the light receiving element positioned opposite to this driven light emitting element. Furthermore, a memory unit is employed to store the coordinate signal. A comparison is made by a coordinate signal comparing device whether or not the previous coordinate signal stored in this memory unit is equal to a coordinate signal newly output from the signal detecting device, and when the equal coordinate signals are continuously detected by the coordinate signal comparing device at a predetermined number, an error signal is output from an error output device.