Abstract: A hydrocyclone separator includes a separator body having an upper body part and a lower body part narrower than the upper body part in diameter; a feeder connected helically to the upper body part from a lateral side for feeding in a raw liquid; an upstream outlet disposed axially within the separator body, having an upper part projecting upward and axially from the upper body part and a lower part extending into the lower body part; a downstream outlet attached axially to the lower body part in spatially communication therewith; and a filtering unit disposed axially within an inner wall confining the upstream outlet. The filtering unit has an upper part projecting upwardly and outwardly from a top end of the upstream outlet and a lower part extending into the downstream outlet. The filtering unit consists of a filtering membrane having an inner wall confining the filtering member.