There are provided a gas blowing nozzle adapted such that, by the fact that a groove-like notch structure has been provided in a side to which a beam IB comes flying in a nozzle tip part of a gas gun used on the occasion of a beam assist deposition or a beam assist etching, the beam IB can pass through an inside of the notch structure, and a charged particle beam apparatus having the gas blowing nozzle 11 as well as a working method.