1. A crimped fiber comprising a polyolefin as a main component, the crimped fiber containing substantially a single raw material, and having an interface in a cross section perpendicular to a fiber length direction.
2. A spunbonded nonwoven fabric comprising the crimped fiber according to claim 1.
3. A method for manufacturing the crimped fiber according to claim 1, the method comprising:
ejecting a polyolefin-based resin from a dumbbell-shaped nozzle having two circular ejecting holes different in area.
4. The method according to claim 3, wherein areas of the two circular ejecting holes of the dumbbell-shaped nozzle satisfy a relationship of a large diameter ejecting hole area/a small diameter ejecting hole area (an area ratio) of 1.2 or more.
5. The method according to claim 3 or 4, wherein a fiber group obtained by ejecting the polyolefin-based resin from the dumbbell-shaped nozzle is cooled with cooling air from

two directions opposite with respect to a side of the fiber group, or with cooling air from three or more directions symmetric about the side of the fiber group.
6. The method according to claim 3 or 4, wherein a fiber group obtained by ejecting the polyolefin-based resin from the dumbbell-shaped hozzle is naturally cooled.
7. A method for manufacturing the spunbonded nonwoven fabric according to claim 2, the method comprising:
collecting the crimped fiber manufactured by the method according to any one of claims 3 to 6 immediately below spinning; and
compression-bonding the crimped fiber using a pair of rolls to form a sheet.