Noninvasive mechanical ventilation (NIMV) has been widelyapplied to the patient with respiratory failure since 1990’s aroundthe world. The respiratory function of the patient with respiratoryfailure should be supported by using positive pressure ventilationuntil primary problem of the patient is treated. Positive pressureshould be given noninvasively or invasively. If the patient isconscious (except unconsiousness due to CO2 retention) and hasintact bulber function(sufficient cough reflex and swallowingfunction) and has stable clinical picture, we have to use NIMVinstead of invasive mechanical ventilation (IMV). NIMV can beapplied to the patient outside of the intensive care unit. The sideeffects of mechanical ventilation are significantly decreased duringNIMV than that of IMV.