A sensor control board, comprising: an image sensor to conduct photo-electric conversion on an inputted signal and to output a photoelectrically converted signal; a signal buffer circuit, comprising an emitter follower circuit comprising a buffer to conduct a buffering operation for transmitting a signal to a subsequent unit, to receive the signal output from the image sensor and to transmit the signal to a subsequent unit; an analog processing circuit to receive the signal from the signal buffer circuit to conduct signal processing including signal amplification and analog/digital (A/D) conversion of the received signal; and a buffer control circuit (43', 430, 430') to conduct an ON/OFF control of the emitter follower circuit; wherein the signal buffer circuit further comprises a variable impedance device connected in series to the output side of the buffer, wherein the variable impedance device is at low impedance when the buffer is conducting the buffer operation and at high impedance when the buffer is not conducting the buffering operation; and a resistor or a second variable impedance device connected between an input side and an output side of the buffer, wherein the resistance of the resistor is smaller than the insulation resistance between the base-emitter of the emitter follower circuit and set to a constant value that does not affect the normal operation of the emitter follower circuit and the second variable impedance device is at a high impedance when the buffer is conducting the buffer operation, and the second variable impedance device is at a low impedance when the buffer is not conducting the buffering operation, and wherein the buffer control circuit comprises: a first switching device to conduct an ON/OFF control of power source supply to the emitter follower circuit; and a second switching device to conduct an ON/OFF control of the first switching device, an ON/OFF control of the second switching device is controlled by a delay signal controllable at a given timing. an image sensor to conduct photo-electric conversion on an inputted signal and to output a photoelectrically converted signal; a signal buffer circuit, comprising an emitter follower circuit comprising a buffer to conduct a buffering operation for transmitting a signal to a subsequent unit, to receive the signal output from the image sensor and to transmit the signal to a subsequent unit; an analog processing circuit to receive the signal from the signal buffer circuit to conduct signal processing including signal amplification and analog/digital (A/D) conversion of the received signal; and a buffer control circuit (43', 430, 430') to conduct an ON/OFF control of the emitter follower circuit; wherein the signal buffer circuit further comprises a variable impedance device connected in series to the output side of the buffer, wherein the variable impedance device is at low impedance when the buffer is conducting the buffer operation and at high impedance when the buffer is not conducting the buffering operation; and a resistor or a second variable impedance device connected between an input side and an output side of the buffer, wherein the resistance of the resistor is smaller than the insulation resistance between the base-emitter of the emitter follower circuit and set to a constant value that does not affect the normal operation of the emitter follower circuit and the second variable impedance device is at a high impedance when the buffer is conducting the buffer operation, and the second variable impedance device is at a low impedance when the buffer is not conducting the buffering operation, and wherein the buffer control circuit comprises: a first switching device to conduct an ON/OFF control of power source supply to the emitter follower circuit; and a second switching device to conduct an ON/OFF control of the first switching device, an ON/OFF control of the second switching device is controlled by a delay signal controllable at a given timing. a first switching device to conduct an ON/OFF control of power source supply to the emitter follower circuit; and a second switching device to conduct an ON/OFF control of the first switching device, an ON/OFF control of the second switching device is controlled by a delay signal controllable at a given timing.