To provide an electron-emitting device and its drive method for obtaining a stable electron-emitting current over a long period from an early stage to a late stage for driving an electron-emitting element.

For example, for driving a surface-transmission electron emitting element 101, a current flowing through the element 101 and its voltage are detected by a current detector 102 and a voltage detector 103, and the product of the detected current and the voltage is calculated by a multiplier 104. The difference between the power amount calculated by the multiplier 104 and a prescribed power setting value is calculated by a subtracter 105, and the element 101 is driven so as to make the calculated difference zero by controlling an applied voltage calculating current 106 and a power amplifier circuit 107.