An ionization vacuum gauge which has at least three electrodes of a grid (2), an electron source (3) and an ion collector (1) in a vacuum vessel (4) connected in communication with a vacuum apparatus, oscillates electrons emitted from the electron source (3) within and outside of the grid (2), ionizes gas molecules flying into the grid (2) by the oscillated electrons, supplements the ionized ions by the ion collector (1) to convert into a current signal, and measures a gas molecular density (pressure) in the vacuum apparatus according to the obtained current intensity, wherein the ion collector (1) is provided with heating means for heating the ion collector.