A wafer counter device comprising a system for aligning the orientation flats of plural wafers in a cassette with one another and a system provided with optical sensors for detecting whether or not the wafers are present in the cassette and serving to count the number of the wafers in the cassette on the basis of the result detected by the optical sensors. The wafers aligning system includes aligning rollers contacted with the rims of the wafers to rotate the wafers, a system for lifting the aligning rollers in such a way that the rollers can be contacted with the rims of the wafers, and a motor for rotating the aligning rollers.