The present invention provides a nanofiber manufacturing method and a nanofiber manufacturing device. A solution 25 in which a polymer is dissolved in a solvent is supplied from a distal end of a nozzle 16 to form a Taylor cone 44 at a distal end opening 16b. By applying a voltage between the solution 25 and a collector 50 using a power supply portion 62, an electrospinning jet 45 is sprayed from the Taylor cone 44 to the collector 50. At the start or stop of electrospinning, a blocking member 48 is inserted into a spraying area 42 of the electrospinning jet 45 such that an unstable electrospinning jet or unstable nanofibers are received. A product is not manufactured from an unstable electrospinning jet formed at the start or stop of electrospinning, and the manufacturing of a defective product is prevented.