PURPOSE: To obtain a low-cost encoder featuring a simple constitution and a reduced number of the component parts by forming the circuit with connection of each tansistor base to each of n pieces of the lateral axes.

CONSTITUTION: Diodes 41∼48 function as the encoder which produces the 4-bit digital signal from the signals sent from the collectors of PNP transistors Tr29∼ 32 via operation of keys 1∼16 and the signals sent from resistances 33∼40. When switch 1 is turned on, the base of Tr29 is grounded via resistance 37. As a result, base current i1 and collector current i2 flow, and "0, 0, 0, 0" are delivered from output terminals A, B, C and D each. Then with turn-on of switch 2, both base current i3 and collector current i2 flow with the output emerging at terminal D via diode 48, and "0, 0, 0, 1" are delivered to terminals A∼D. When switch 16 is turned on in the same way, current i4 and i5 flow with emergence of "1, 1, 1, 1" at terminals A∼D.