A nonwoven fabric is constructed of a highly flat glass fiber which is a glass fiber whose section is flat and has a flatness ratio of 2.0 to 10 and which has such a section that the packing fraction is at least 85%, preferably at least 90%. In this nonwoven fabric, the glass fiber section has a shape near rectangle, and hence, the glass fibers can be arranged very densely to form a thin nonwoven fabric having a high bulk density, and when it is used as a laminate material, the glass fiber content can be increased and the surface smoothness can simultaneously be enhanced and can be used appropriately as a reinforcing material for a printed wiring board. Moreover, the above flat glass fiber can be produced by use of, for example, a nozzle having such a shape that one side of the major axis walls of a nozzle chip having a flat nozzle hole is partly notched.