Disclosed is a parallel filtering circuit comprising at least two filters of a depth layer filtering type connected in parallel to each other in conduits showing different fluid resistances respectively, whereby, even when both the filters are clogged with particles of contaminants, the total flow rate may not decrease sharply, so that a preventive measure can be immediately taken before a fatal situation occurs. An orifice may be connected at its inlet to the outlet of the conduit having a smaller fluid resistance and at its outlet to the outlet of the conduit having a having fluid resistance.