Abstract: A filter comprises at least one filtration unit with a filtration passage having an inlet and an outlet, wherein the filtration unit includes at least one groove formed in an inlet side surface of the filtration unit, said at least one groove extending to the inlet and dimensioned to hold back substances which may clog the filtration passage, by means of upper edges of said at least one groove. According to the present invention, by forming at least one groove in an inlet side surface of the filtration unit, the filtration passages of the filter can be effectively prevented from being clogged.