PURPOSE: To express gradation with high stability, by setting a part of a recorder to a detection needle to detect the resistance value of a resistor layer and changing the energy applied to a head corresponding to the output of the resistance value.

CONSTITUTION: Resistance is measured by bringing the detection needle (sensor) on a head into contact with the resistor layer of a current supply sheet under pressure. A microcomputer receives two values of the detected voltage V1 from a sensor 1 and the detected voltage V2 from a sensor 2 to operate or judge a proper value and sends a feedback signal to a voltage control circuit. The voltage control circuit changes voltage corresponding to said signal. Herein, since the microcomputer takes the average of the detected voltages V1, V2, the average detected voltage becomes almost constant. Therefore, if this value is used to send the feedback signal to the voltage control circuit of the next stage, a stable feedback system can be constructed.