PURPOSE: To make it possible to cope with the modification request of a key array easily by enabling a micro-processor to detect the key number of a depressed key by scanning the key martrix in the sequence of key numbers and by obtaining the corresponding code signal from a code table.

CONSTITUTION: In ROM4, a program is stored which makes processor 3 encode, and in ROM5, codes are stored sequentially which correspond to the key array of key matrix 1. Further, register 8 scans on key matrix 1 and by its output, binary code decimal decoder 10 makes one of key arrays R0...R7 of key matrix "L". As a result, the key matrix is scanned in the order of key numbers by using processor 3 to detect the key number of the depressed key, and the code signal equivalent to the key number of the depressed key is outputted from the code table stored with code signals in the order of key numbers. Consequently, it is made possible to cope with the modification request of the key arrays, etc., easily