A vacuum ejector comprising: a supply port supplied with compressed air; a vacuum port connected to a suction unit; a vacuum generation mechanism configured to generate negative pressure due to an effect of supply air supplied from the supply port; a break valve configured to supply break air to the vacuum port; a supply flow path configured to connect the supply port and the vacuum generation mechanism, and including a supply valve therein; a negative pressure flow path configured to connect the vacuum generation mechanism and the vacuum port; a break flow path configured to connect the break valve and the negative pressure flow path; and a seal valve mechanism arranged in the negative pressure flow path between the vacuum generation mechanism and the break flow path, and configured to prevent the break air that passes through the break flow path to be supplied to the vacuum port from flowing out to the vacuum generation mechanism, wherein the seal valve mechanism is configured to enter an open state due to supply of the supply air from the supply valve, and enter a closed state when the supply of the supply air from the supply valve stops, characterized in that the seal valve mechanism includes: a seal opening formed by constricting a diameter of the negative pressure flow path; a valve plug configured to be biased toward the seal opening from the break flow path side to block the seal opening; and a piston portion configured to receive pressure of the supply air to move the valve plug in a direction away from the seal opening. a supply port supplied with compressed air; a vacuum port connected to a suction unit; a vacuum generation mechanism configured to generate negative pressure due to an effect of supply air supplied from the supply port; a break valve configured to supply break air to the vacuum port; a supply flow path configured to connect the supply port and the vacuum generation mechanism, and including a supply valve therein; a negative pressure flow path configured to connect the vacuum generation mechanism and the vacuum port; a break flow path configured to connect the break valve and the negative pressure flow path; and a seal valve mechanism arranged in the negative pressure flow path between the vacuum generation mechanism and the break flow path, and configured to prevent the break air that passes through the break flow path to be supplied to the vacuum port from flowing out to the vacuum generation mechanism, wherein the seal valve mechanism is configured to enter an open state due to supply of the supply air from the supply valve, and enter a closed state when the supply of the supply air from the supply valve stops, characterized in that the seal valve mechanism includes: a seal opening formed by constricting a diameter of the negative pressure flow path; a valve plug configured to be biased toward the seal opening from the break flow path side to block the seal opening; and a piston portion configured to receive pressure of the supply air to move the valve plug in a direction away from the seal opening. a seal opening formed by constricting a diameter of the negative pressure flow path; a valve plug configured to be biased toward the seal opening from the break flow path side to block the seal opening; and a piston portion configured to receive pressure of the supply air to move the valve plug in a direction away from the seal opening.