This filter is used to purify air by removing foreign matters such as liquid droplets contained in the air. A separation unit (23) is formed with a port block (13) and a separation cylinder (20), and the port block is formed with a primary port (11) and a secondary port (12). From the secondary port (12), the air purified by removing the foreign matters in a separation chamber (25) of the separation unit (23) is flowed out. A discharge pipe (37) for guiding the purified air to the secondary port (12) is disposed in a center portion of a swirl flow generating chamber (24). The foreign matters discharged from the discharging port (31) are collected in a collection container (27). In the collection container (27), a baffle plate 51 having a liquid guiding surface (50) is provided. A fin (52) is provided in an outer peripheral portion of the baffle plate (51), and the liquid guiding surface (50) positioned at a center portion of the baffle plate (51) is flat.