A vacuum measurement device includes a grid (10) and an electron source (20) provided inside a vacuum vessel, and an ion beam (100) extracted outside the grid is captured by an ion collector (40) and is converted into a current signal. The grid (10) is a grid-shaped cylinder, and an ion outlet (11) is opened and elongated in the longitudinal direction along the side surface of the grid (10). The vacuum measurement device includes a primary ion collector (40) capturing specific ions and a secondary ion collector (50) capturing other ions. The gas molecule density of the ion source is obtained from a total current of the primary and secondary ion collectors, and a ratio of the gas molecule density of the specific ions relative to the gas molecule density is obtained from a ratio of the current of the primary ion collector (40) relative to the total current.