Abstract: Four fingers of a hand of an individual person, i.e. the index finger, the middle finger, the medical finger and the little finger are placed on a transparent measuring table in juxtaposition. A guide member is also placed on the table to restrict the position of the hand and light is irradiated onto the table. The intensity of the light passed through the transparent measuring table is scanned by a television camera and so on at every light receiving point to convert it an electrical signal. Thus obtained electric signals are processed to calculate the differential data of the finger lengths thereby detecting an individual person.