This filter is used for purifying air by removing foreign matters such as liquid droplets contained in the air. A separation unit is formed by a primary port, a port block to which a secondary port is formed, and a separation cylinder attached to the port block. Inside a swirl flow generating chamber of the separation unit, a cylinder blade portion formed by arranging a plurality of blades, which are extended in an axial direction along an inner peripheral surface and also inclined in a circumferential direction, in a cylindrical form is provided. The air flowed into the swirl flow generating chamber is caused to be a swirl flow by the cylindrical blade portion and foreign matters such as liquid droplets are discharged toward a collection container in a separation chamber. The purified air is guided from a discharge pipe to the secondary port.