₅n7 An exhaust apparatus and a vacuum pumping unit using the exhaust apparatus are disclosed. The exhaust apparatus comprises a thermionic emission source, an electron accelerating grid surrounding the thermionic emission source, an outer electrode surrounding the electron accelerating grid, an ion accelerating grid intersecting an axis of the outer electrode and installed apart from the outer electrode, a vessel containing the thermionic emission source, the electron accelerating grid, the outer electrode, and the ion accelerating grid therein, a magnet disposed outside of the vessel and generating a magnetic field almost parallel to the axis of the outer electrode, a power supply for heating the thermionic emission source, a first DC power supply for applying a voltage between the electron accelerating grid, the outer electrode and the thermionic emission source, a second DC power supply for applying a voltage between the outer electrode and the ion accelerating grid so as to get the outer electrode positive. The vacuum pumping unit is constituted by interposing the exhaust apparatus between a vacuum vessel to be evacuated and an auxiliary vacuum pump. By this, gas molecules in the vacuum vessel are ionized by electron bombardment and accelerated toward the auxiliary vacuum pump to be exhausted.