PURPOSE: To obtain ultrafine fiber-producing type conjugate fiber, containing a conjugate part having an island-in-sea type structure producing ultrafine fibers having a specific size or below and other conjugate parts having a larger size, having a high breaking strength and capable of providing stable spinnability in production.

CONSTITUTION: Ultrafine fiber-producing type conjugate fiber obtained by removing a sea component 3 constructing an island-in-sea structure with a solvent, then composing the fiber from an island-in-sea type conjugate part 1 capable of producing ≤0.1d size and other conjugate parts 4 having ≤0.5d size and exposing the island-in-sea type conjugate part to the surface of the conjugate fiber and providing ≥1d size of the total conjugate fiber. The above-mentioned fiber has a high breaking strength and is capable of providing stable spinnability due to conjugate spinning with other parts having excellent spinnability. A nonwoven fabric obtained by using the aforementioned fiber has an ultrahigh breaking strength.