To arrange filaments highly in a perpendicular direction.

A nozzle 3 for extruding a filament 11 and slits 6a, 6b for jetting high speed air flow for thinning the filament 11 extruded from the nozzle 3 are installed on a melt blow die 1. The thinned filament 11 is collected on a conveyor 7 and conveyed as a web. An air flow vibration mechanism 9 which is rotated in the direction of an arrow A around a shaft 9a is provided in a high speed air flow region between the melt blow die 1 and the conveyor 7. The high speed air is flown by rotating the air flow vibration mechanism 9 and the filament 11 is periodically vibrated in the conveying direction.