PURPOSE: To electrically read key information expressing the positions and shapes of indented grooves by generating a timing signal for each advance of a key for a predetermined length along the key groove and outputting a signal expressing the shape of the key in synchronization with the timing signal.

CONSTITUTION: Timing signal light-emitting diodes 3a to 3f and key code light- emitting diodes 2a, 2f face each other by clamping a key hole 1a and are optically coupled through the light receiving elements and optical fibers. Then, the key K is inserted to the main body 1, timing signals are sequentially output from the light receiving elements 12a, 12b...12f every time when the tip of the key reaches Q1, Q2...Q6, the switching circuits 17, 18 are turned ON, and key information passes to the encoding circuits 19, 20. Moreover, key information reading the position and shape of each indented groove of the key in the memory 21 is input as digital data and compared to the key information already stored and unlocking is permitted if both of them coincide each other.