To provide an electron emitting device having a low gate reactive current which can be preferably used for a power amplifier having a high input resistance, a linear transfer characteristic and a high mutual conductance.

The electron emitting device has a first substrate and a second substrate positioned face to face, an electron emitting part formed on the first substrate, a first electrode positioned higher than the first substrate so that the first electrode and the first substrate face each other sandwiching the electron emitting part in a cross sectional view, and a second electrode positioned higher than the first electrode so that the second electrode and the first electrode face each other sandwiching the electron emitting part in a horizontal view. The electron emitting device is characterized in that when a voltage is applied to the first electrode, the electron emitting part emits electron vertically to the first substrate and the electron reaches the second substrate. It is another character of the electron emitter that the amount of electron reaching the second substrate is controlled by the second electrode. The electron emitting device is further characterized in that the second substrate has a third electrode facing the electron emitting part.