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 . <EOS>