A horizontal driving circuit for a flat display device, the horizontal driving circuit comprising a buffer circuit and a precharge circuit, the buffer circuit comprising a constant current circuit, a switch, and a source follower transistor, wherein the source follower transistor is arranged to receive a voltage depending on the gradation voltage at its gate, and to output, at its source, an output signal for a signal line of the flat display device, the constant current circuit is connected to the source of the source follower transistor, the output of the precharge circuit is connectable to the signal line, and the switch is provided between the source of the source follower transistor and the output of the precharge circuit, wherein the horizontal driving circuit is configured to turn off the switch during a precharge period, and to turn on the switch after the precharge period, the precharge circuit is configured to set the signal line to a predetermined potential in the precharge period, and to output the output signal of the buffer circuit to the signal line received through the switch after the precharge period, characterized in that: the constant current circuit comprises a first transistor forming a reference current source, a second transistor whose drain is connected to the reference current source, a sampling capacitor connected between a gate and a source of the second transistor, a first switch connected between the drain and the gate of the second transistor, and a second switch connected between the drain of the second transistor and the source follower transistor, wherein the horizontal driving circuit is configured to set a voltage across the sampling capacitor equal to the gate-source voltage (Vgs) of the second transistor produced when the second transistor is driven by a reference current of the reference current source, and the horizontal driving circuit is configured to turn off the first transistor of the constant current circuit to stop the supply of a reference current, to disconnect the sampling capacitor from the drain of the second transistor by turning off the first switch, as well as to connect, by turning on the second switch, the drain of the second transistor to the source follower transistor which is a driving target of the constant current circuit causing a current to flow out from the source follower transistor by means of the gate-source voltage (Vgs) of the second transistor which is set in the sampling capacitor, and the constant current circuit is configured to repeat a period for setting the voltage across the sampling capacitor and a period for driving the driving target, and the period for setting the voltage across the sampling capacitor is set as a period in the precharge period. the constant current circuit comprises a first transistor forming a reference current source, a second transistor whose drain is connected to the reference current source, a sampling capacitor connected between a gate and a source of the second transistor, a first switch connected between the drain and the gate of the second transistor, and a second switch connected between the drain of the second transistor and the source follower transistor, wherein the horizontal driving circuit is configured to set a voltage across the sampling capacitor equal to the gate-source voltage (Vgs) of the second transistor produced when the second transistor is driven by a reference current of the reference current source, and the horizontal driving circuit is configured to turn off the first transistor of the constant current circuit to stop the supply of a reference current, to disconnect the sampling capacitor from the drain of the second transistor by turning off the first switch, as well as to connect, by turning on the second switch, the drain of the second transistor to the source follower transistor which is a driving target of the constant current circuit causing a current to flow out from the source follower transistor by means of the gate-source voltage (Vgs) of the second transistor which is set in the sampling capacitor, and the constant current circuit is configured to repeat a period for setting the voltage across the sampling capacitor and a period for driving the driving target, and the period for setting the voltage across the sampling capacitor is set as a period in the precharge period.