PURPOSE: To reduce the power consumption of LED by the control of a pulse interval due to a monostable circuit without receiving excessive influence of external noise in transmission, by converting a mechanical displacement amount to the change of electrostatic capacity while further converting the change amount to an optical signal to transmit the same.

CONSTITUTION: The titled apparatus is equipped with measuring apacitors CA, CB each differentially changed in the capacity amount thereof corresponding to mechanical displacement, the charging and discharging circuits R1, R2 thereof, transistors (TR) T1, T2, detection circuits FF, Q1, Q2 each set when charging voltage exceeds a predetermined level and a bistable circuit Q3 driven by the detection outputs of said detection circuits. In place of controlling TR.T3 by the output signal V3 of FF Q2, ON/OFF control is performed through a monostable circuit. When LED is lighted over the ON-period of an output signal 1/3, power consumption is increased and, therefore, voltage with short pulse amplitude is respectively supplied corresponding to the H-state or the L-state of the output signal V3 from the monostable circuit and the power consumption of LED is reduced.