A filtration device (1; 2) comprising: a filter element that includes a filter medium, a first plate, and a second plate, the filter medium having a hollow cylindrical shape with openings at both ends, the first plate covering the opening at an upper end of the filter medium, the second plate covering the opening at a lower end of the filter medium; a filter case having a bottomed substantially cylindrical shape that is internally provided with the filter element; and a lid member covering an opening at an upper end of the filter case, wherein the first plate includes a first tubular portion (34c; 34c-1) having a substantially cylindrical shape, and the first tubular portion (34c; 34c-1) protrudes toward the lid member with the filter element inserted into the filter case, the lid member includes ribs (25a; 25a-1; 25a-2), and the first tubular portion (34c; 34c-1) includes a first projection protruding outward in a radial direction, characterised in that the lid member further includes a second tubular portion having a substantially cylindrical shape, the ribs (25a; 25a-1; 25a-2) are provided radially outwardly of the second tubular portion and protrude in the same direction as the second tubular portion, the second tubular portion is configured to be inserted into a hollow portion of the first tubular portion (34c; 34c-1), when the second tubular portion is inserted into the first tubular portion (34c; 34c-1), the ribs (25a; 25a-1; 25a-2) are provided along an outer circumferential surface of the first tubular portion (34c; 34c-1), notches (25d; 25d-1) are provided between the ribs (25a; 25a-1; 25a-2), and with the lid member attached to the first plate, the second tubular portion is inserted into the first tubular portion (34c; 34c-1) and the first projection is inserted into a corresponding one of the notches (25d; 25d-1) between the ribs (25a; 25a-1; 25a-2). a filter element that includes a filter medium, a first plate, and a second plate, the filter medium having a hollow cylindrical shape with openings at both ends, the first plate covering the opening at an upper end of the filter medium, the second plate covering the opening at a lower end of the filter medium; a filter case having a bottomed substantially cylindrical shape that is internally provided with the filter element; and a lid member covering an opening at an upper end of the filter case, wherein the first plate includes a first tubular portion (34c; 34c-1) having a substantially cylindrical shape, and the first tubular portion (34c; 34c-1) protrudes toward the lid member with the filter element inserted into the filter case, the lid member includes ribs (25a; 25a-1; 25a-2), and the first tubular portion (34c; 34c-1) includes a first projection protruding outward in a radial direction, characterised in that the lid member further includes a second tubular portion having a substantially cylindrical shape, the ribs (25a; 25a-1; 25a-2) are provided radially outwardly of the second tubular portion and protrude in the same direction as the second tubular portion, the second tubular portion is configured to be inserted into a hollow portion of the first tubular portion (34c; 34c-1), when the second tubular portion is inserted into the first tubular portion (34c; 34c-1), the ribs (25a; 25a-1; 25a-2) are provided along an outer circumferential surface of the first tubular portion (34c; 34c-1), notches (25d; 25d-1) are provided between the ribs (25a; 25a-1; 25a-2), and with the lid member attached to the first plate, the second tubular portion is inserted into the first tubular portion (34c; 34c-1) and the first projection is inserted into a corresponding one of the notches (25d; 25d-1) between the ribs (25a; 25a-1; 25a-2).