A compound line filter comprising a bobbin, two coils (210, 220) and a magnetic core, wherein the coils (210, 220) have been wound on the bobbin in a state of being separated from each other in an axial direction that corresponds to a winding direction of the coils; the magnetic core (300, 300A) comprises a closed magnetic path part and a secondary magnetic path part (340, 340A); the bobbin is attached to the closed magnetic path part; the bobbin comprises two gears; the two gears are positioned between the coils (210, 220) in the axial direction; the closed magnetic path part comprises a winding core part (310, 310A) extending in the axial direction and a primary magnetic path part coupling both ends of the winding core part (310, 310A) to each other; the secondary magnetic path part (340, 340A) extends from the primary magnetic path part in a protruding direction perpendicular to the axial direction and is positioned between the coils (210, 220) in the axial direction; the bobbin is rotatably attached to the winding core part (310, 310A); the secondary magnetic path part (340, 340A) is positioned between a portion of the primary magnetic path part and the winding core part in the protruding direction; each gear and the secondary magnetic path part (340, 340A) overlap with each other when viewed along the axial direction; the bobbin is formed with a plurality of flanges to position the coils (210, 220); the plurality of flanges includes two inner flanges positioned at the innermost positions in the axial direction in between the two coils; between the inner flanges in the axial direction, the two gears are formed; the secondary magnetic path part (340, 340A) is positioned between the two gears in the axial direction; the two gears face each other when viewed along the axial direction; the gears each have the same shape; and each of the two gears is disposed to be plane symmetric with respect to a plane perpendicular to the axial direction, characterized in that the bobbin is undivided in the axial direction; the compound line filter further comprises two partition plates (424, 424A); the partition plates (424, 424A) are provided on both sides of the secondary magnetic path part (340, 340A) in the axial direction and positioned between the coils (210, 220) in the axial direction and each of the two gears overlaps with one of the partition plates (424, 424A) at least in part when viewed from the protruding direction. the coils (210, 220) have been wound on the bobbin in a state of being separated from each other in an axial direction that corresponds to a winding direction of the coils; the magnetic core (300, 300A) comprises a closed magnetic path part and a secondary magnetic path part (340, 340A); the bobbin is attached to the closed magnetic path part; the bobbin comprises two gears; the two gears are positioned between the coils (210, 220) in the axial direction; the closed magnetic path part comprises a winding core part (310, 310A) extending in the axial direction and a primary magnetic path part coupling both ends of the winding core part (310, 310A) to each other; the secondary magnetic path part (340, 340A) extends from the primary magnetic path part in a protruding direction perpendicular to the axial direction and is positioned between the coils (210, 220) in the axial direction; the bobbin is rotatably attached to the winding core part (310, 310A); the secondary magnetic path part (340, 340A) is positioned between a portion of the primary magnetic path part and the winding core part in the protruding direction; each gear and the secondary magnetic path part (340, 340A) overlap with each other when viewed along the axial direction; the bobbin is formed with a plurality of flanges to position the coils (210, 220); the plurality of flanges includes two inner flanges positioned at the innermost positions in the axial direction in between the two coils; between the inner flanges in the axial direction, the two gears are formed; the secondary magnetic path part (340, 340A) is positioned between the two gears in the axial direction; the two gears face each other when viewed along the axial direction; the gears each have the same shape; and each of the two gears is disposed to be plane symmetric with respect to a plane perpendicular to the axial direction, characterized in that the bobbin is undivided in the axial direction; the compound line filter further comprises two partition plates (424, 424A); the partition plates (424, 424A) are provided on both sides of the secondary magnetic path part (340, 340A) in the axial direction and positioned between the coils (210, 220) in the axial direction and each of the two gears overlaps with one of the partition plates (424, 424A) at least in part when viewed from the protruding direction.