PURPOSE: To obtain an individual identifier which uses no magnetic card by writing directly the secret data on a piezoelectric element sensor for read of characters/marks.

CONSTITUTION: A piezoelectric element sensor 1 for read of characters/marks detects the pen pressure in the form of a pen pressure to output an electrical output. In other words, each of patterns forming the secret data is drawn with a prescribed locus fed to each piezoelectric element. When each piezoelectric element detects the pressure along the corresponding locus the secret data are converted into electrical signals via the piezoelectric element, and sent to a data collation processing part 2. Then the part 2 extracts the registered secret data out of a memory part 3 and collates it with the secret data supplied from the sensor 1. The result of this collation is outputted through an output part 4.